Paint Calculator

A paint calculation is a precise mathematical framework used to determine the exact volumetric quantity of architectural coating required to cover a specific surface area to a standard uniform thickness. This calculation is vital in both residential and commercial construction because it prevents the costly waste of over-purchasing while eliminating the severe aesthetic risks associated with under-purchasing, such as color-matching discrepancies between different manufacturing batches. By mastering the variables of spread rate, surface porosity, and application methodology, anyone can transform a chaotic guesswork process into a predictable, highly accurate material procurement strategy.

What It Is and Why It Matters

A paint calculation is the systematic process of translating three-dimensional room dimensions into a two-dimensional surface area, and subsequently converting that area into a liquid volume measurement based on the specific physical properties of the coating being applied. At its core, this framework solves a fundamental logistical problem in interior design, home improvement, and commercial contracting: bridging the gap between physical space and liquid material requirements. Without a rigorous mathematical approach, individuals are forced to rely on visual estimation, which consistently results in significant errors. Buying too much paint ties up capital, creates hazardous waste disposal issues, and clutters storage spaces with rapidly degrading chemicals.

Conversely, buying too little paint introduces catastrophic risks to the project's final quality. Paint is manufactured in massive industrial vats, and despite stringent quality control, microscopic variations in pigment dispersion mean that two different batches of the exact same color code will often have a visible color shift, known in the industry as a Delta-E difference. If a painter runs out of material three-quarters of the way through a wall and purchases a new gallon from a different batch, the transition line will be glaringly obvious under normal lighting conditions. Therefore, calculating the exact required volume upfront allows the practitioner to "box" or mix all the paint together in a single large container before starting, ensuring absolute color uniformity across the entire architectural space. This mathematical discipline separates professional tradespeople from amateurs, ensuring efficient capital allocation and flawless aesthetic execution.

History and Origin of Paint Measurement

The necessity of calculating paint volume traces its origins back to the mid-19th century, coinciding with the industrialization of architectural coatings. Prior to the 1860s, painters were essentially chemists who mixed their own materials on the job site using raw linseed oil, white lead powder, and natural earth pigments. Because they mixed small, customized batches continuously throughout the day, the concept of calculating a total project volume in advance was largely irrelevant. However, the paradigm shifted drastically in 1866 when the Sherwin-Williams Company pioneered the first ready-mixed, reliably standardized liquid paints sold in fixed volumetric containers. This commercialization forced consumers and contractors alike to purchase material in predefined quantities—specifically the United States liquid gallon, defined legally as exactly 231 cubic inches of volume.

Once paint became a packaged commodity, the need to predict consumption birthed the modern spread rate metric. Early 20th-century paint manufacturers began printing "coverage per gallon" estimates on their tin labels to help consumers navigate this new purchasing model. These early paints, heavily reliant on dense lead carbonates, offered vastly different coverage rates than modern formulations. The mathematical models had to evolve again in the 1970s following the federal ban on lead-based paints in the United States (1978). The industry transitioned to acrylic latex formulations utilizing titanium dioxide as the primary hiding pigment. Because titanium dioxide scatters light differently and creates a different dry film thickness, the industry standard coverage rate settled into the modern benchmark of 350 to 400 square feet per gallon. Today, the calculation has been digitized and refined, incorporating variables like application mechanics and surface porosity, but it remains rooted in the 19th-century transition from bespoke mixing to standardized commercial manufacturing.

Key Concepts and Terminology

To accurately calculate paint requirements, one must intimately understand the specialized vocabulary that dictates how liquid coatings behave in the physical world. Ignoring these variables inevitably leads to flawed calculations and compromised finishes.

Spread Rate and Volume Solids

The Spread Rate (or Coverage Rate) is the total surface area that one unit of liquid paint (typically a gallon or liter) can cover uniformly. For standard interior premium acrylic latex paint, the industry standard spread rate is strictly defined as 350 to 400 square feet per gallon. However, this rate is heavily dictated by Volume Solids. Volume solids represent the percentage of the paint that remains on the wall after the water and chemical solvents evaporate. A cheap paint might have 25% volume solids, meaning 75% of the liquid evaporates, leaving a microscopically thin layer that requires three coats to hide the underlying surface. A premium paint with 45% volume solids leaves a much thicker layer, achieving opacity in fewer coats and radically altering the total volume calculation.

Dry Film Thickness (DFT) and Wet Film Thickness (WFT)

Professional estimators calculate paint not just by area, but by depth. Wet Film Thickness (WFT) is the depth of the liquid paint immediately after application, measured in mils (one-thousandth of an inch). Dry Film Thickness (DFT) is the depth of the coating after fully curing. The calculation of paint volume is ultimately an exercise in achieving a specific DFT—usually 1.5 to 2.0 mils per coat for standard interior walls. If a painter applies the material too thinly to stretch a gallon further than the calculated spread rate, the DFT drops below the manufacturer's specification, resulting in a structurally weak film that will scuff, fade, and fail prematurely.

Porosity and Substrate

The Substrate is the underlying surface being painted, and its Porosity—its ability to absorb liquid—is a critical multiplier in the calculation. A perfectly sealed, previously painted wall has low porosity and will yield the maximum 400 square feet per gallon. Conversely, bare, unprimed drywall or raw masonry acts like a sponge. These highly porous substrates will pull the solvents into the wall, reducing the spread rate of the first coat to as little as 200 square feet per gallon. Understanding substrate porosity dictates whether the mathematical formula requires a heavy deduction in the spread rate or the inclusion of a dedicated primer coat.

How It Works — Step by Step

The mathematical mechanics of calculating paint volume require a systematic, sequential approach. The process involves calculating the gross surface area, subtracting the non-paintable voids, factoring in the coverage rate, multiplying by the required number of coats, and adding a strict waste contingency.

The Core Formulas

1. Gross Wall Area = (Length of Wall 1 + Length of Wall 2 + Length of Wall 3 + Length of Wall 4...) × Ceiling Height
2. Non-Paintable Area = (Number of Standard Doors × 21 sq ft) + (Number of Standard Windows × 15 sq ft)
3. Net Paintable Area = Gross Wall Area - Non-Paintable Area
4. Base Gallons per Coat = Net Paintable Area / Spread Rate (typically 350 sq ft)
5. Total Required Gallons = (Base Gallons per Coat × Number of Coats) × 1.10 (10% Waste Factor)

Full Worked Example

Consider a homeowner preparing to paint the interior walls of a primary bedroom. The room measures 14 feet wide by 18 feet long. The ceiling height is exactly 9 feet. The room features two standard entry/closet doors and three standard windows. The homeowner is applying a premium acrylic latex paint (spread rate of 350 sq ft/gal) and requires two complete coats for proper durability and color depth.

Step 1: Calculate Gross Wall Area First, determine the linear perimeter of the room: 14 + 18 + 14 + 18 = 64 linear feet. Multiply the perimeter by the ceiling height: 64 feet × 9 feet = 576 square feet of Gross Wall Area.

Step 2: Calculate Non-Paintable Area Standard interior doors account for 21 square feet each (including the trim). Standard windows account for 15 square feet each. Doors: 2 doors × 21 sq ft = 42 sq ft. Windows: 3 windows × 15 sq ft = 45 sq ft. Total Non-Paintable Area: 42 + 45 = 87 square feet.

Step 3: Calculate Net Paintable Area Subtract the non-paintable voids from the gross area. 576 sq ft (Gross) - 87 sq ft (Non-Paintable) = 489 square feet of Net Paintable Area.

Step 4: Calculate Base Gallons per Coat Divide the net area by the manufacturer's spread rate. 489 sq ft / 350 sq ft per gallon = 1.397 gallons required for a single coat.

Step 5: Calculate Total Required Gallons Multiply by the number of coats, then add the mandatory 10% waste factor. 1.397 gallons × 2 coats = 2.794 gallons. 2.794 gallons × 1.10 (Waste Factor) = 3.073 gallons.

Because paint is sold in discrete gallon increments, the homeowner must round up to the nearest whole gallon. The precise, mathematically sound purchasing decision is exactly 4 gallons of paint.

Types, Variations, and Methods

While the core mathematical principles of surface area remain constant, the methodology of paint calculation fractures into several distinct variations based on the nature of the architectural surface and the mechanical method of application. Each variation requires specific mathematical adjustments to the baseline formulas.

Interior vs. Exterior Calculations

Interior calculations are generally straightforward, dealing with flat, two-dimensional planes of drywall or plaster. Exterior calculations, however, introduce complex geometric multipliers. When calculating paint for exterior lap siding (clapboard), the overlapping nature of the boards creates a larger surface area than the flat two-dimensional footprint of the wall. Estimators must apply a 1.15 multiplier (adding 15%) to the gross wall area to account for the bottom edges and the angled faces of lap siding. For heavy corrugated metal or deep board-and-batten siding, this multiplier increases to 1.20 (20%). Failing to apply these geometric multipliers on exterior projects guarantees a severe material shortage.

Roller Application vs. Airless Spraying

The mechanical method of transferring the paint from the bucket to the wall drastically impacts the required volume. Traditional application using a 3/8-inch nap synthetic roller is highly efficient, transferring approximately 95-98% of the liquid directly to the substrate. Therefore, the standard 350 sq ft/gal spread rate applies perfectly. Conversely, commercial contractors frequently utilize high-pressure airless sprayers to increase labor speed. Airless sprayers atomize the paint into a fine mist, which inherently results in "overspray"—paint particles that drift away on air currents or fall to the floor rather than adhering to the wall. When calculating paint volume for an airless sprayer application, the estimator must apply a 20% to 30% loss factor to the total volume. A room that mathematically requires 10 gallons via roller will require 12.5 to 13 gallons when sprayed.

Primer vs. Finish Coats

Calculations must strictly separate primer from finish paints. Primer is chemically formulated with higher concentrations of binders and lower concentrations of pigments; its job is to seal the surface, not to provide color. When calculating primer for new drywall, the estimator must use a reduced spread rate of 250 to 300 square feet per gallon, as the porous paper facing of the drywall will absorb a massive amount of the liquid. Once the primer coat is calculated and applied, the surface is now sealed, meaning the subsequent finish coats can be calculated at the standard 350 to 400 square feet per gallon spread rate.

Real-World Examples and Applications

To fully grasp the utility of accurate paint calculation, one must examine how these mathematical principles scale across different real-world scenarios, from small residential tasks to massive commercial undertakings. The math remains identical, but the financial implications multiply exponentially.

Scenario 1: The Residential Color Change A homeowner decides to paint their 400-square-foot living room. The room has 8-foot ceilings, yielding a perimeter of 80 linear feet and a gross wall area of 640 square feet. After subtracting two large sliding glass doors (80 sq ft total) and one entry door (21 sq ft), the net paintable area is 539 square feet. The critical variable here is color: the homeowner is transitioning the walls from a dark navy blue to a pale, off-white linen color. Even with premium paint, a drastic dark-to-light transition mathematically requires three full coats to achieve total opacity without the dark base showing through. Calculation: 539 sq ft / 350 sq ft/gal = 1.54 gallons per coat. 1.54 gallons × 3 coats = 4.62 gallons. Adding a 10% waste factor yields 5.08 gallons. The homeowner must purchase 6 gallons of the off-white paint to successfully execute this drastic color shift.

Scenario 2: The Commercial Stucco Exterior A painting contractor is bidding on a 3,500-square-foot single-story commercial building. The exterior substrate is heavy "dash" stucco, a highly textured, aggressive surface. The gross exterior wall area (perimeter × height) measures 3,200 square feet. Because heavy stucco has massive peaks and valleys, its actual three-dimensional surface area is drastically larger than its two-dimensional footprint. The contractor must apply a 1.50 multiplier (adding 50% more area) to account for the texture. Calculation: 3,200 sq ft × 1.50 = 4,800 effective square feet. The contractor intends to spray the building, requiring an additional 25% overspray loss factor. Base gallons for one coat: 4,800 / 350 = 13.71 gallons. Adding 25% overspray: 13.71 × 1.25 = 17.13 gallons per coat. For a standard two-coat commercial application, the contractor must procure 35 gallons of exterior masonry paint. If the contractor had ignored the stucco multiplier and the overspray factor, they would have budgeted for only 18 gallons, resulting in a catastrophic financial loss on the contract.

Common Mistakes and Misconceptions

The landscape of paint estimation is fraught with pervasive myths and amateur errors that consistently lead to compromised projects. Eradicating these misconceptions is vital for achieving professional-grade results.

The "One-Coat Coverage" Myth

The single most destructive misconception in architectural painting is the belief in "one-coat coverage." Paint manufacturers frequently market premium lines as "one-coat guarantees." However, this is a highly conditional marketing claim, not a mathematical reality. One-coat coverage is only physically possible when repainting a surface with the exact same color, over a perfectly sealed substrate, using a meticulously applied, ultra-thick wet film. In 98% of real-world applications—especially when changing colors or painting over patched drywall—the chemistry of titanium dioxide simply cannot achieve full optical hiding in a single 1.5-mil dry film layer. Calculators who build their volumetric models based on a single coat will inevitably run out of material, forcing them to buy more paint from a different batch, risking severe color-matching failures. Professional calculations always mandate a minimum of two finish coats.

Subtracting Small Voids

Amateurs frequently attempt to calculate their non-paintable areas with exhaustive, microscopic precision. They will measure every single electrical outlet, light switch, heating register, and small decorative niche, subtracting these tiny square footages from their gross wall area. This is a severe mathematical error. The paint saved by not painting a 3-inch by 5-inch electrical box is entirely consumed by the heavy saturation of the roller nap and the paint left clinging to the inside of the bucket. Subtracting tiny voids artificially lowers the required volume, eating directly into the project's safety margin. The strict professional rule is to only subtract major architectural voids: standard doors, large windows, and massive built-in cabinetry. Everything else is treated as solid, paintable wall space.

Ignoring Ceiling Paint Mechanics

When homeowners calculate paint for a room, they often calculate the walls meticulously but treat the ceiling as an afterthought. A common mistake is assuming ceiling paint covers at the same 400 square feet per gallon rate as premium wall paint. In reality, ceiling paint is formulated with extremely high levels of calcium carbonate to achieve a dead-flat finish that hides drywall seams. This formulation makes ceiling paint inherently thicker and less spreadable, often dropping the actual coverage rate to 250 or 300 square feet per gallon. Furthermore, ceilings are painted against gravity, leading to heavier roller saturation and more micro-splatter waste. Calculations for ceiling surfaces must utilize a reduced spread rate to ensure adequate material procurement.

Best Practices and Expert Strategies

Mastering paint calculation extends beyond the raw mathematics; it requires the implementation of strict logistical protocols that professional estimators use to guarantee flawless execution and absolute color consistency.

The 10% Waste Contingency

Every professional paint calculation must end by multiplying the final volumetric requirement by 1.10, adding a mandatory 10% waste contingency. This is not arbitrary padding; it is a mathematical necessity. Paint is lost at every stage of the application process. Approximately 2% remains permanently adhered to the interior walls of the plastic bucket. Another 3% is absorbed into the synthetic fibers of the roller covers and the bristles of the cutting-in brushes. An additional 2-3% is lost to micro-splatter and accidental drips. Finally, a small reserve must be retained in a sealed, climate-controlled container for future touch-ups. Without this 10% contingency factored into the initial purchase, the applicator will inevitably scrape the bottom of the bucket on the final wall, compromising the dry film thickness to stretch the material.

The "Boxing" Protocol

The most critical expert strategy tied to paint calculation is the practice of "boxing." Because the calculation yields the exact total volume required (e.g., 5 gallons), the professional will purchase those 5 gallons and immediately pour them all together into a single, clean 5-gallon commercial bucket. They will then mechanically mix the entire volume before applying a single drop to the wall. This protocol completely neutralizes the Delta-E color variations that occur between different manufacturing batches. If an amateur calculates they need 3 gallons and paints directly out of the individual 1-gallon cans, they risk a slight color shift halfway across a prominent wall when they open the second can. Accurate upfront calculation is the prerequisite that makes whole-room boxing possible.

Laser Measurement and Precision

Professional estimators do not rely on pacing out a room or using flexible, sagging tape measures to determine gross wall area. The industry standard practice is to utilize a digital laser distance measurer. By placing the laser against one wall and shooting the beam to the opposite wall, the estimator acquires the linear dimension accurate to within 1/16th of an inch. This eliminates the compounding errors that occur when rounding room dimensions up or down. A room estimated loosely at "about 15 by 20" has a perimeter of 70 feet; if the actual laser measurement is 16.5 by 21.5, the perimeter is 76 feet. On a 10-foot ceiling, that 6-foot perimeter discrepancy equals 60 square feet of uncalculated wall space—nearly a quarter of a gallon of paint missing from the final calculation.

Edge Cases, Limitations, and Pitfalls

While the standard mathematical models apply flawlessly to 90% of architectural scenarios, there are specific edge cases where the baseline formulas break down entirely. Recognizing these limitations is crucial for preventing severe miscalculations.

Acoustic "Popcorn" Ceilings

Calculating paint volume for heavily textured acoustic ceilings (commonly known as "popcorn" ceilings) requires a complete abandonment of standard spread rates. The aggregate material used to create the acoustic texture acts essentially as a sponge, while simultaneously creating a massive three-dimensional surface area. If an estimator uses the standard 350 sq ft/gal metric on a virgin, unpainted acoustic ceiling, they will run out of material before completing half the room. The strict rule for unpainted acoustic ceilings is to calculate the square footage and divide by a maximum spread rate of 150 to 200 square feet per gallon. Furthermore, these ceilings must be sprayed rather than rolled, as the mechanical friction of a paint roller will tear the water-soluble acoustic texture right off the drywall.

Drastic Color Transitions and Deep Bases

The mathematical limitation of paint coverage is heavily exposed when dealing with "deep base" colors—vibrant reds, deep yellows, and stark blacks. Standard light-colored paints utilize a "white base" heavily loaded with titanium dioxide, which provides massive optical hiding power. Deep, vibrant colors cannot use a white base (otherwise the red would become pink), so they utilize a "clear base" loaded exclusively with liquid colorants. Clear bases have virtually zero inherent hiding power. If a mathematical calculation assumes a standard two-coat coverage for a vibrant primary red over a white wall, the project will fail. Deep base colors routinely require a tinted gray primer followed by three to four full topcoats to achieve visual solidity. The calculator must double the anticipated volume when specifying highly saturated, clear-base colors.

The Drywall Level 5 Finish Pitfall

In high-end luxury construction, walls are often finished to a "Level 5" standard, meaning the entire surface of the drywall paper is skim-coated with a millimeter-thick layer of joint compound to create a glass-smooth surface. While this sounds ideal for painting, it presents a massive calculation pitfall. Joint compound is infinitely more porous than standard drywall paper. If a Level 5 wall is not sealed with a high-solids PVA (polyvinyl acetate) drywall primer, the first coat of expensive finish paint will be instantly sucked into the microscopic pores of the compound, flashing unevenly and reducing the spread rate to less than 200 square feet per gallon. The mathematical model assumes a properly primed substrate; if the substrate preparation is skipped, the volumetric calculation becomes entirely invalid.

Industry Standards and Benchmarks

The calculation of architectural coatings is not a subjective art; it is governed by strict numerical standards established by global trade organizations. Understanding these benchmarks allows one to evaluate their own calculations against professional-grade criteria.

The MPI and PDCA Standards

The Master Painters Institute (MPI) and the Painting and Decorating Contractors of America (PDCA) publish the definitive architectural standards used in commercial blueprints and government contracts. According to PDCA Standard P5-09, a properly executed interior paint job requires a minimum Dry Film Thickness (DFT) of 1.2 to 1.5 mils per coat, achieved through the application of one primer coat and two finish coats. To achieve this specific DFT, the MPI dictates that the theoretical spread rate of standard architectural latex must not exceed 400 square feet per gallon under any circumstances. If a contractor's bid indicates they are stretching the material to 500 square feet per gallon, they are in direct violation of industry standards, resulting in a substandard, ultra-thin film that will fail durability testing.

Waste Factor Benchmarks

Industry standards also dictate strict benchmarks for material waste based on the application method, which must be hard-coded into any professional calculation. The standard benchmark for brush and roller application is a 10% to 15% loss factor. For conventional air spray (using a compressor), the benchmark loss factor is a staggering 40%. For high-pressure airless spray application, the benchmark is strictly set at 20% to 30% loss. Commercial estimators utilize specialized software that automatically applies these specific loss benchmarks to the raw square footage calculations, ensuring that the procurement order matches the physical realities of fluid dynamics and atomization.

Comparisons with Alternatives

While the precise mathematical calculation of surface area (Gross Area minus Voids divided by Spread Rate) is the definitive method for determining paint volume, there are alternative estimation heuristics used in the industry. Comparing these methods highlights why the strict mathematical approach remains superior.

The Floor-Area Multiplier Method

Many real estate agents and quick-turnaround contractors use a rapid heuristic known as the Floor-Area Multiplier. Instead of measuring individual walls, they take the floor square footage of a room and multiply it by a fixed constant—typically 2.5 for rooms with 8-foot ceilings, or 3.0 for rooms with 9-foot ceilings. For example, a 200-square-foot bedroom (10x20) multiplied by 2.5 yields an estimated 500 square feet of wall space. Pros: This method is incredibly fast and requires only a single floor measurement, making it useful for rough ballpark budgeting on massive multi-unit apartment complexes. Cons: It is wildly inaccurate for specific material procurement. It fails to account for large voids like double-doors or floor-to-ceiling windows, and it breaks down completely in rooms with non-standard geometry, vaulted ceilings, or open-concept floor plans. Relying on this multiplier for actual purchasing frequently leads to overbuying material by 20% or more.

The Visual "Eyeball" Estimation

The most common alternative employed by amateur DIYers is simply standing in a room and guessing based on past experience—"This looks like a two-gallon room." Pros: It requires zero mathematical effort or measurement tools. Cons: Human spatial reasoning is notoriously terrible at estimating two-dimensional surface area wrapped around a three-dimensional volume. Visual estimation almost universally results in under-purchasing, leading to the dreaded mid-project hardware store run and the subsequent color-matching failures discussed earlier. The strict mathematical calculator eliminates human spatial bias, relying entirely on the immutable laws of geometry and fluid volume.

Frequently Asked Questions

Do I really need to calculate and purchase primer separately from my finish paint? Yes, absolutely. Primer and finish paint are chemically distinct products designed for entirely different purposes. Primer is rich in binders designed to seal porous surfaces (like new drywall or raw wood) and block stains, while finish paint is rich in pigments designed to provide color and a durable, washable shell. If you calculate your total volume assuming you can just use extra finish paint as a primer, you will waste expensive material. Finish paint will soak into a porous wall unevenly, requiring three or four coats to achieve the uniform sheen that one coat of cheap primer and two coats of finish paint would achieve.

How do I calculate the paint required for baseboards, crown molding, and window trim? Trim is calculated using linear feet rather than square feet, because the surface area is extremely narrow. Measure the entire perimeter of the room's baseboards, add the linear length of all window and door casings, and add the crown molding. The industry standard benchmark is that one gallon of premium semi-gloss trim enamel will cover approximately 350 to 400 linear feet of standard 4-inch to 6-inch trim. Because trim is usually painted with a brush, the transfer efficiency is very high, but you should still add a 10% waste factor to your final linear calculation.

Should I subtract the square footage of my kitchen cabinets when calculating wall paint? Yes. Kitchen cabinetry represents a massive architectural void that permanently obscures the wall behind it. If you have a 15-foot wall that features upper and lower cabinets spanning 10 feet of that length, calculating the gross wall area without subtracting the cabinets will result in purchasing drastically more paint than necessary. Measure the total square footage of the installed cabinetry (width times height) and subtract it from the gross wall area, exactly as you would a large window.

What happens if I calculate perfectly, but I have half a gallon left over? Having a half-gallon of leftover paint is actually the precise goal of a perfect calculation; it represents your 10% waste and touch-up contingency. You should never throw this paint away. Seal the can tightly by placing a layer of plastic wrap over the opening before hammering the lid down, which prevents the solvent from evaporating. Store this remainder in a climate-controlled area (never in a freezing garage or a boiling attic). You will mathematically require this exact batch-matched reserve to touch up scuffs, drywall repairs, and moving damage over the next three to five years.

Does the sheen (finish) of the paint affect the volumetric calculation? Indirectly, yes. While a gallon of flat paint and a gallon of high-gloss paint contain the same liquid volume, their optical properties alter how many coats you might need. Flat or matte paints absorb light, which inherently hides drywall imperfections and overlapping roller marks, often allowing for solid visual coverage in exactly two coats. High-gloss paints reflect light, acting like a mirror that highlights every microscopic flaw and variation in film thickness. Because of this, achieving a flawless high-gloss finish often requires a third mathematically calculated coat to ensure the dry film thickness is perfectly uniform across the entire wall.

How do I calculate paint for a vaulted or triangular ceiling wall? When a wall follows the pitch of a vaulted ceiling, it forms a complex geometric shape—usually a rectangle with a triangle sitting on top of it. To calculate this accurately, break the wall into two separate shapes. First, calculate the rectangular base (Width × Height up to the point where the angle begins). Then, calculate the triangular upper section using the geometric formula for a triangle: (Width × Height of the triangular section) ÷ 2. Add the area of the rectangle and the area of the triangle together to find the gross square footage of that specific vaulted wall, then proceed with your standard coverage rate division.