Paper Size Reference

A paper size reference is the standardized system of physical dimensions used for manufacturing, printing, and designing paper products across the globe. Understanding these precise dimensions is crucial for graphic designers, publishers, architects, and everyday professionals to ensure their digital layouts translate perfectly to physical media without distortion, unwanted cropping, or printing errors. This comprehensive guide will explore the elegant mathematics behind international standards, the historical development of regional formats, and the exact dimensional formulas and best practices you need to master print design and document formatting.

What It Is and Why It Matters

At its core, a paper size reference is a universal dictionary of physical dimensions that dictates the exact width and height of sheets of paper used in everyday life, commercial printing, and specialized industries. Without standardized paper sizes, the modern world would face insurmountable logistical nightmares. Imagine a scenario where every manufacturer produced printers, binders, envelopes, and filing cabinets to arbitrary dimensions. A document printed in one office might not fit into an envelope purchased from a local store, and a blueprint drafted in Tokyo might be impossible to reproduce accurately on a plotter in New York. Standardized paper sizes solve this problem by establishing a rigorous, predictable framework that hardware manufacturers, software developers, and paper mills all adhere to.

This standardization matters immensely because it bridges the gap between digital intent and physical reality. When a graphic designer sets up a canvas in Adobe InDesign or a student opens a new Microsoft Word document, the software defaults to a specific paper size—usually A4 or US Letter. If the designer does not understand the physical constraints of these sizes, their carefully crafted layout might be ruined when sent to a commercial printer. Text might run off the edge of the page, images might be scaled disproportionately, or the final product might require expensive custom trimming. By understanding paper sizes, professionals can design with confidence, knowing exactly how their work will manifest in the real world.

Furthermore, understanding paper sizes is an economic necessity. The commercial printing industry operates on razor-thin margins and relies heavily on efficiency. Standard paper sizes allow paper mills to produce massive rolls of paper that can be cut down into standard sheets with zero waste. When designers request custom sizes that do not align with these standard cuts, the printer must discard the offcuts, passing the cost of that wasted material directly to the client. By aligning projects with established paper size references, businesses can save thousands of dollars on large print runs, streamline their shipping and mailing processes, and ensure cross-border compatibility in an increasingly globalized economy.

History and Origin

The concept of standardizing paper sizes dates back centuries, but the elegant mathematical system used by the majority of the world today has a highly specific origin. On October 25, 1786, the German physicist and mathematician Georg Christoph Lichtenberg wrote a letter to Johann Beckmann detailing the practical and aesthetic advantages of an aspect ratio of the square root of two ($1:\sqrt{2}$). Lichtenberg noted that paper with this proportion possessed a unique geometric property: when folded in half parallel to its shortest sides, the two resulting halves maintained the exact same aspect ratio as the original sheet. Despite this brilliant observation, the idea lay dormant for over a century, as paper making remained a highly localized and unstandardized craft throughout the 1800s.

The true birth of the modern international paper size system occurred in the aftermath of World War I. In 1922, Dr. Walter Porstmann, a German engineer and mathematician, resurrected Lichtenberg's concept and formalized it into a comprehensive system of paper sizes for the Deutsches Institut für Normung (DIN). This standard, known as DIN 476, established the A-series of paper sizes, beginning with a base sheet (A0) that had an area of exactly one square meter and an aspect ratio of $1:\sqrt{2}$. The system was so logical and efficient that it rapidly spread beyond Germany. By the mid-20th century, it had been adopted by dozens of countries, and in 1975, it was officially enshrined as an international standard by the International Organization for Standardization under the designation ISO 216.

In stark contrast, the development of North American paper sizes was driven by historical accident and industrial inertia rather than mathematical elegance. The origins of the US Letter size (8.5 by 11 inches) are somewhat murky, tracing back to the dimensions of molds used by early paper makers. In 1921, a committee established by US Secretary of Commerce Herbert Hoover attempted to standardize paper sizes for government use, settling on 8 by 10.5 inches. However, the commercial sector largely ignored this, sticking to the 8.5 by 11-inch format. It wasn't until the early 1980s, under the Reagan administration, that the US government finally capitulated to commercial reality and officially adopted 8.5 by 11 inches as the standard for all federal documents. Today, the United States, Canada, and parts of Mexico remain the only major holdouts against the ISO 216 standard, creating a persistent dual-system reality in global publishing.

How It Works — Step by Step

The Mathematics of ISO 216

The brilliance of the ISO 216 system lies in its mathematical foundation. The entire A-series is built upon two immutable rules. First, the aspect ratio (the ratio of the width to the height) of every sheet must be exactly $1:\sqrt{2}$, which is approximately 1 to 1.4142. Second, the base size of the series, denoted as A0, must have a surface area of exactly one square meter ($1 \text{ m}^2$). Because of the $1:\sqrt{2}$ aspect ratio, whenever you cut or fold an A-series sheet in half across its longest dimension, the resulting two sheets will have the exact same proportions as the original. This means that artwork can be scaled up or down between any A-series sizes without any stretching, squishing, or cropping.

Calculating the Dimensions of A0

To find the exact dimensions of A0 in millimeters, we set up a system of algebraic equations. Let $x$ be the width of the paper and $y$ be the height. We know the area is $1 \text{ m}^2$, which is $1,000,000 \text{ mm}^2$. We also know the ratio of $y$ to $x$ is $\sqrt{2}$. Equation 1: $x \times y = 1,000,000$ Equation 2: $y = x\sqrt{2}$ Substitute Equation 2 into Equation 1: $x \times (x\sqrt{2}) = 1,000,000$ $x^2\sqrt{2} = 1,000,000$ $x^2 = \frac{1,000,000}{1.41421356}$ $x^2 \approx 707,106.78$ $x = \sqrt{707,106.78} \approx 840.896$ millimeters. By ISO rounding rules, this is rounded to the nearest millimeter: $x = 841 \text{ mm}$. To find $y$, we multiply $x$ by $\sqrt{2}$: $y = 841 \times 1.41421356 \approx 1189.35$ millimeters. Rounded to the nearest millimeter, $y = 1189 \text{ mm}$. Therefore, the definitive size of A0 is 841 mm by 1189 mm.

Worked Example: Deriving A4 from A0

To find the dimensions of any subsequent size (A1, A2, A3, A4), you simply take the dimensions of the previous size, halve the larger number, and keep the smaller number as the new larger number. Let us derive the world's most common paper size, A4, starting from our A0 dimensions of 841 mm × 1189 mm. Step 1 (A1): Halve the length of A0 (1189 / 2 = 594.5, rounded to 594). The new size is 594 mm × 841 mm. Step 2 (A2): Halve the length of A1 (841 / 2 = 405.5, rounded to 420). The new size is 420 mm × 594 mm. Step 3 (A3): Halve the length of A2 (594 / 2 = 297). The new size is 297 mm × 420 mm. Step 4 (A4): Halve the length of A3 (420 / 2 = 210). The new size is 210 mm × 297 mm. Thus, an A4 sheet is exactly 210 mm wide by 297 mm high. This simple halving process ensures that the aspect ratio remains constant, and it allows anyone with a calculator to determine the exact dimensions of any ISO paper size instantly.

Key Concepts and Terminology

To navigate the world of paper sizes and commercial printing, you must understand the specialized vocabulary used by designers and printers. Aspect Ratio is the proportional relationship between the width and height of a sheet of paper. As established, the ISO standard uses a $1:\sqrt{2}$ ratio, while North American sizes use arbitrary ratios (e.g., US Letter is 8.5:11, or roughly 1:1.294). Trim Size refers to the final, finished dimensions of a printed piece after it has been cut down from a larger press sheet. When a client asks for an A4 brochure, 210 mm × 297 mm is the trim size.

Bleed is a critical concept in print design that is inextricably linked to paper size. Because industrial cutting machines (guillotines) have a slight margin of error (usually 1 mm to 2 mm), printing an image exactly to the trim edge risks leaving a thin, unintended white line along the border of the paper. To prevent this, designers extend the artwork beyond the trim size by a standard amount—usually 3 mm (or 0.125 inches in the US). This extra area is the bleed. Therefore, to produce a final A4 document (210 × 297 mm) with edge-to-edge color, the designer must create a digital canvas that is 216 mm × 303 mm (adding 3 mm to all four sides).

Basis Weight and GSM measure the thickness and density of the paper, which often dictates which paper sizes are appropriate for a given project. GSM stands for Grams per Square Meter. Because the ISO system is based on an A0 sheet being exactly one square meter, a paper rated at 80 GSM means that a single A0 sheet of that paper weighs exactly 80 grams. Since A4 is one-sixteenth the area of A0, a single sheet of 80 GSM A4 paper weighs exactly 5 grams (80 / 16). In North America, the system is much more confusing; Basis Weight is measured in pounds (lbs) and refers to the weight of 500 sheets (a ream) of the paper in its basic, uncut manufacturing size, which varies depending on the type of paper (e.g., Bond paper has a different basic size than Cover stock).

Types, Variations, and Methods

The ISO Series: A, B, and C

The international paper size standard is divided into three main series to accommodate different use cases. The A-series (A0 to A10) is the primary standard used for general printing, stationery, and publications. A4 is the standard letterhead, A3 is used for small posters or spreadsheets, and A5 is common for notepads and paperback books.

The B-series was introduced to provide intermediate sizes for applications where the A-series jumps were too drastic. The dimensions of a B-series sheet are the geometric mean of the A-series sheet of the same number and the A-series sheet of the next larger number. For example, the dimensions of B4 are the geometric mean of A4 and A3. B-series sizes are slightly larger than their A-series counterparts and are heavily used in the publishing industry for printing books, as well as for passports and large posters (like B2, which is 500 mm × 707 mm).

The C-series is specifically designed for envelopes. The dimensions of a C-series size are the geometric mean of the A and B sizes of the same number. This mathematical relationship creates a perfect nesting system. An A4 letter fits perfectly into a C4 envelope without folding. If you fold that A4 letter in half once (making it A5 size), it fits perfectly into a C5 envelope. If you fold it into thirds, it fits into a DL envelope (a special size measuring 110 mm × 220 mm, heavily used for business correspondence).

North American Sizes

The North American system relies on traditional formats rather than mathematical formulas. The most common size is Letter (8.5 × 11 inches / 215.9 × 279.4 mm), used for almost all standard office documents. Legal size (8.5 × 14 inches / 215.9 × 355.6 mm) is used primarily for contracts and real estate documents, providing extra length for signatures and addendums. Tabloid or Ledger size (11 × 17 inches / 279.4 × 431.8 mm) is exactly the size of two Letter sheets placed side-by-side, making it ideal for newsletters, menus, and small engineering drawings.

Architectural and Engineering Sizes

In the United States, architects and engineers use specialized size series. The ANSI series (American National Standards Institute) ranges from ANSI A (which is identical to Letter, 8.5 × 11 inches) up to ANSI E (34 × 44 inches). The Arch series is preferred by architects because its aspect ratios align better with standard architectural scales (like 1/4 inch = 1 foot). The Arch series ranges from Arch A (9 × 12 inches) up to Arch E (36 × 48 inches). These sizes are specifically engineered so that large blueprints can be rolled or folded neatly into standard filing systems.

Real-World Examples and Applications

To understand how paper sizes dictate professional workflows, consider a 30-year-old graphic designer tasked with creating a marketing campaign for a European client. The campaign requires a large promotional poster, a standard corporate brochure, and a small hand-out flyer. Because the designer is working within the ISO system, they can design a single master artwork file at A1 size (594 mm × 841 mm) for the poster. Because the aspect ratio is universally $1:\sqrt{2}$, the designer can simply scale that exact same digital file down by 50% to print the A3 brochures (297 mm × 420 mm), and scale it down again to print the A5 flyers (148 mm × 210 mm). No artwork needs to be repositioned, and no text will be unexpectedly cropped off the edges. The mathematical harmony of the A-series saves the designer hours of layout adjustments.

Contrast this with a North American scenario. An event coordinator is designing a program booklet. They decide to use a standard 11 × 17 inch Tabloid sheet, folded in half to create a booklet with 8.5 × 11 inch Letter-sized pages. If the coordinator wants to scale this exact design down to a smaller, pocket-sized booklet, they run into a problem. If they fold an 8.5 × 11 inch Letter sheet in half, they get a "Half-Letter" size measuring 5.5 × 8.5 inches. The aspect ratio of Letter is 1.294, while the aspect ratio of Half-Letter is 1.545. Because the proportions change drastically, the coordinator cannot simply shrink the digital file. They must manually open the document, resize the text boxes, rearrange the photographs, and adjust the margins to fit the new, narrower proportion.

In the publishing industry, paper sizes dictate the economics of book printing. A publisher looking to print a standard trade paperback will often choose a trim size of 6 × 9 inches (a standard US book size). To print this economically, the commercial printer will use a massive web press that feeds paper from a continuous roll. The width of that roll is carefully matched to a multiple of the 6 × 9 inch trim size (plus bleed and margins). If the author insists on a custom size of 6.5 × 9.5 inches, the printer might have to use the exact same paper roll but fit fewer pages across its width, resulting in massive amounts of blank paper being trimmed off and thrown away. This custom size could increase the cost of a 10,000-copy print run by $3,000 to $5,000 simply due to paper waste.

Common Mistakes and Misconceptions

One of the most pervasive mistakes made by beginners and even intermediate professionals is assuming that US Letter and A4 are interchangeable. Because they look similar to the naked eye, users frequently design a document in US Letter (8.5 × 11 inches / 215.9 × 279.4 mm) and send it to an international partner who prints it on A4 paper (8.27 × 11.69 inches / 210 × 297 mm). Because A4 is narrower and taller than US Letter, the printer will either crop the sides of the document (cutting off text) or scale the entire document down to fit the narrower width, resulting in awkward, oversized top and bottom margins. When conducting international business, always verify the destination's paper standard before finalizing a PDF.

Another major misconception involves the relationship between digital pixels and physical paper size. Beginners often create a digital canvas measured in pixels (e.g., 1920 × 1080) and assume it will print at a specific physical size. However, pixels have no physical dimension until they are assigned a resolution, measured in DPI (Dots Per Inch) or PPI (Pixels Per Inch). To print a US Letter document (8.5 × 11 inches) at a high-quality commercial standard of 300 PPI, the digital file must be exactly 2550 pixels wide (8.5 × 300) by 3300 pixels high (11 × 300). Attempting to print a 1920 × 1080 pixel image at US Letter size will result in a blurry, pixelated mess because the effective resolution drops to roughly 174 PPI.

Finally, novices frequently misunderstand the concept of "borderless printing." Many people design a document with color extending all the way to the edge of the screen and expect their home office printer to replicate it perfectly. In reality, 95% of consumer and office laser printers have an unprintable margin—a mechanical limitation where the printer's rollers grip the paper. This margin is typically 4 mm to 6 mm wide. If a design requires edge-to-edge color, it cannot be printed directly at the target size on an office printer. It must be printed on a larger sheet of paper (with bleed) and manually trimmed down to the final size using a guillotine or craft knife.

Best Practices and Expert Strategies

Expert print designers operate on a fundamental rule: always begin a project by defining the final physical trim size and the required bleed. Before a single line of text is written or a single image is placed, the digital workspace must be configured correctly. If you are designing an A4 magazine cover, your document setup in Adobe Illustrator or InDesign should be set to a width of 210 mm and a height of 297 mm, with a dedicated bleed setting of 3 mm on all sides. This creates a clear visual boundary for the "trim box" (where the paper will be cut) and the "bleed box" (where the background art must extend).

Another crucial strategy is the implementation of a "safe area" or "margin." Even with precise industrial cutting, slight shifts happen during the printing and trimming process. Experts establish a safe area at least 5 mm (or 0.25 inches) inside the trim line. Absolutely no critical information—such as text, logos, or crucial parts of a photograph—should extend past this safe area. If a logo is placed 1 mm from the trim edge, a slight shift in the guillotine blade could slice off the edge of the logo, ruining the professional appearance of the document.

When preparing documents for international distribution, experts utilize a strategy called "universal formatting." If a company needs a PDF manual that will be printed by users in both the United States (on Letter paper) and Europe (on A4 paper), the designer will create a custom page size that accommodates both. Since Letter is wider (215.9 mm vs 210 mm) and A4 is taller (297 mm vs 279.4 mm), a designer can use a page size of 210 mm × 279.4 mm, or simply use massive margins on a standard A4 layout. By keeping all critical content within an 8 × 10.5 inch bounding box, the document can be printed on either A4 or Letter paper using the "Fit to Page" printer setting without losing any content or looking awkwardly off-center.

Edge Cases, Limitations, and Pitfalls

While standardized paper sizes are incredibly robust, they break down in specific edge cases, particularly when dealing with raw paper manufacturing. When a commercial printer produces an A4 booklet, they do not feed individual A4 sheets into their massive offset presses. They feed large sheets that contain multiple A4 pages arranged in a grid (a process called imposition). However, because the printer needs room for bleed, crop marks, and the mechanical "gripper edge" of the press, they cannot use standard A-series paper for the raw material. This necessitates an entirely different standard: the SRA (Supplementary Raw format A) series. SRA paper is slightly larger than standard A paper. For example, SRA3 measures 320 mm × 450 mm, providing ample room to print two A4 pages (with bleed and crop marks) and then trim them down to the perfect final size. A common pitfall for novice print buyers is purchasing standard A-series paper in bulk and bringing it to a commercial printer, only to find out the paper is too small to accommodate the necessary bleeds and mechanical margins.

Another significant limitation involves paper grain. Paper is manufactured on a fast-moving wire mesh, causing the cellulose fibers to align in the direction the machine is moving. This creates a "grain direction" in the paper. Paper folds easily and cleanly parallel to the grain, but folding against the grain causes the paper fibers to crack, resulting in an ugly, jagged fold line. When specifying paper sizes for a project that involves folding (like a greeting card or a brochure), you must specify the grain direction. A size might be listed as 11 × 17 inches (grain short) or 17 × 11 inches (grain long). If a designer ignores grain direction when laying out a complex folded brochure, the final product will look cheap and damaged, regardless of how perfectly the dimensions were calculated.

Custom die-cuts present another edge case where standard sizes can be misleading. If a client wants a presentation folder shaped like a circle with a diameter of 200 mm, they might assume it fits easily on an A4 sheet (210 mm × 297 mm). However, creating custom shapes requires a physical steel die to stamp out the paper. The die-cutting machine requires significant "grip" space around the edges of the paper to hold it steady during the stamping process. Therefore, a 200 mm circular cut might actually require an SRA4 or A3 sheet of raw paper to process correctly, significantly increasing the material costs beyond what the final dimensions suggest.

Industry Standards and Benchmarks

The undisputed global benchmark for paper sizes is ISO 216, managed by the International Organization for Standardization based in Geneva, Switzerland. This standard strictly defines the A and B series. It is supplemented by ISO 269, which defines the C-series for envelopes, and ISO 217, which dictates the RA and SRA sizes used by commercial printers for untrimmed raw paper. Compliance with ISO 216 is so universal that it is legally mandated for official government documents in almost every country outside of North America.

In the United States, the governing body is the American National Standards Institute (ANSI). The benchmark for technical drawings and engineering documents is ANSI/ASME Y14.1. This standard defines the ANSI A through E sizes. Unlike the ISO system, the ANSI system is based on an alternating aspect ratio. ANSI A (8.5 × 11) has an aspect ratio of 1.294. When you double it to get ANSI B (11 × 17), the aspect ratio becomes 1.545. Double it again to get ANSI C (17 × 22), and the ratio returns to 1.294. This alternating ratio means that engineers cannot simply scale a drawing from ANSI A to ANSI B without adjusting the layout, a significant mathematical disadvantage compared to the ISO system.

For archival and museum standards, paper size intersects with paper composition. The Library of Congress and the ISO 9706 standard dictate that documents intended for long-term preservation must not only conform to standard filing sizes (typically A4 or Letter to fit in standard acid-free archival boxes) but must also have a pH value between 7.5 and 10.0 (acid-free) and a minimum tear resistance. Archival storage boxes are benchmarked exactly to these standard sizes; a box designed for A4 documents will typically have internal dimensions of 220 mm × 310 mm, providing exactly 10 mm of clearance for easy retrieval without bending the paper edges.

Comparisons with Alternatives

When planning a project, the primary alternative to using standard paper sizes is opting for a custom size. The advantage of a custom size is distinctiveness; a square brochure measuring 200 mm × 200 mm stands out immediately in a stack of standard A4 documents. It commands attention and feels premium. However, the disadvantages are entirely economic and logistical. Because all commercial paper is manufactured in rolls or master sheets optimized for standard sizes, producing a 200 mm × 200 mm brochure requires cutting down a larger standard sheet (like A3) and throwing away a massive percentage of the paper as offcuts. This can easily double the paper cost of the project. Furthermore, custom sizes require custom envelopes, which are exponentially more expensive than standard C-series or #10 business envelopes. For 95% of commercial projects, the cost savings of standard sizes far outweigh the aesthetic novelty of custom dimensions.

Another comparison is between the North American system and the ISO system. The North American system is deeply entrenched in the US economy; billions of dollars of filing cabinets, binders, and printers are built strictly for 8.5 × 11-inch paper. For a local US business, using the North American standard is the only logical choice to ensure compatibility with clients and vendors. However, for a multinational corporation, the ISO system is vastly superior. The mathematical consistency of the $1:\sqrt{2}$ aspect ratio saves countless hours in document scaling and formatting. A multinational company standardizing entirely on A4 will face friction in its US offices, but will achieve seamless document exchange across its European, Asian, and South American branches.

Finally, one must compare physical paper sizes to digital-first formats. In the past, documents were designed for physical paper (A4) and then uploaded as PDFs. Today, many documents are designed as "digital-first" alternatives, optimized for screen viewing. A standard 16:9 widescreen monitor has an aspect ratio of 1.77. If a designer creates a digital-first presentation intended only for screens, they will use a 1920 × 1080 pixel canvas. If someone attempts to print this 16:9 digital document onto A4 paper (aspect ratio 1.41), the printer will have to leave massive white bars at the top and bottom of the page. Understanding paper size references allows designers to make conscious choices about whether a document's primary life will be physical or digital, and format accordingly.

Frequently Asked Questions

What is the exact difference between US Letter and A4 paper? US Letter measures 8.5 by 11 inches, which translates to 215.9 mm wide and 279.4 mm high. A4 paper is part of the international ISO 216 standard and measures 210 mm wide and 297 mm high (approximately 8.27 by 11.69 inches). Therefore, A4 is slightly narrower (by about 6 millimeters) and noticeably taller (by about 18 millimeters) than US Letter. This difference means documents formatted tightly for one size will often experience clipping or margin issues when printed on the other without adjustment.

How do I calculate the dimensions of any A-series paper without looking it up? Because the A-series uses a consistent $1:\sqrt{2}$ aspect ratio, each smaller size is exactly half the area of the previous size. To find the next size down, you take the dimensions of your current sheet (e.g., A3 is 297 mm × 420 mm), divide the larger number by two (420 / 2 = 210), and keep the smaller number as is. The new dimensions are 210 mm × 297 mm, which is A4. If dividing results in a decimal, you always round down to the nearest whole millimeter according to ISO standards.

Why is US Legal paper 14 inches long? US Legal paper measures 8.5 by 14 inches. The origin of the 14-inch length is historical, dating back to the days of manual document drafting by lawyers. Lawyers needed extra space at the bottom of standard contracts to add signatures, stamps, and brief handwritten addendums without requiring a second sheet of paper, which could easily become separated and cause legal disputes over contract integrity. The 14-inch length provided this necessary buffer while maintaining the standard 8.5-inch width to fit into standard typewriter carriages.

What size is a standard business card? Business card sizes are not governed by ISO 216 and vary heavily by region. In the United States and Canada, the standard business card is 3.5 × 2 inches (88.9 × 50.8 mm). In Western Europe, the standard is slightly different, typically aligning with credit card dimensions at 85 × 55 mm. In Japan, the standard "Meishi" size is 91 × 55 mm. When designing business cards for international networking, you must adhere to the local standard, as a US business card will often rattle around loosely in a European cardholder, and a Japanese card will simply not fit into a US wallet slot.

How does paper weight (GSM) relate to paper size? GSM stands for Grams per Square Meter. It is a measurement of the paper's density and thickness based on the A0 paper size, which has an area of exactly 1 square meter. If a paper is rated at 100 GSM, a single A0 sheet of that paper weighs exactly 100 grams. Because an A4 sheet is one-sixteenth of an A0 sheet, a single piece of 100 GSM A4 paper weighs exactly 6.25 grams (100 divided by 16). This mathematical relationship allows commercial printers to calculate shipping weights for massive print runs with perfect accuracy.

What are SRA paper sizes used for? SRA stands for Supplementary Raw format A. Commercial printers cannot print edge-to-edge (full bleed) directly onto an A4 sheet because the printing press requires a mechanical grip margin to pull the paper through the rollers, and the design requires extra bleed area to allow for trimming. SRA sizes are slightly larger than standard A sizes (e.g., SRA3 is 320 × 450 mm, whereas A3 is 297 × 420 mm). Printers print the artwork onto the oversized SRA sheet and then use a guillotine to trim the excess paper away, leaving a perfectly sized A-series document with color extending flawlessly to the edges.