Paper sizes from 4A0 down to A10 are not an arbitrary list. They come from one formula, one ratio, and one standard that almost every country outside North America has adopted. Once you understand the logic behind the sequence, remembering every dimension in it becomes almost unnecessary, because you can work most of them out in your head.

This matters far beyond stationery. Architects choosing a sheet size for a floor plan, students formatting an academic poster, and print shops setting up a job all rely on the same underlying system. Getting it wrong wastes paper, distorts scale drawings, and can even cause a document to be rejected at submission stage. The rest of this guide breaks the system down clearly, size by size.

What Are Paper Sizes and Why Do They Follow a Standard?

A paper size is simply a fixed set of width and height dimensions that a sheet of paper is manufactured and cut to, so that printers, publishers, and offices anywhere in the world can rely on the same physical dimensions without measuring each sheet by hand. Before international standards existed, paper sizes varied by country, by mill, and sometimes even by individual print shop, which made it difficult to exchange documents, design equipment, or scale drawings consistently.

The solution most of the world settled on is ISO 216, the international standard published by the International Organization for Standardization that defines the A, B, and C series of paper sizes. Kenya, like most Commonwealth and European countries, follows ISO 216 through its adoption by the Kenya Bureau of Standards, which means the A4 sheet in a Nairobi office is identical in size to the A4 sheet used in Berlin, Tokyo, or Cape Town.

What Is the ISO 216 Standard?

ISO 216 is the international paper size standard that defines the A and B series, based on a simple geometric rule: every sheet keeps the same width to height ratio, so that when you fold or cut a sheet exactly in half along its longer side, the two resulting halves are still the same shape as the original, just smaller. This single rule generates the entire A series from 4A0 down to A10 without needing to define each size independently.

The Origin and History of the A Series Paper Size System

The mathematical foundation of the A series is older than the standard itself. The German scientist Georg Christoph Lichtenberg first described the square root of two ratio for paper in a letter written in 1786, noting that a sheet with that proportion could be halved repeatedly while keeping its shape. It took over a century for the idea to become a working industrial standard.

In 1922, the German engineer Dr. Walter Porstmann formalised the system as the German standard DIN 476, defining A0 as a sheet with an area of exactly one square metre and every subsequent size as a halving of the one before it. DIN 476 spread across Europe through the twentieth century and was eventually adopted internationally as ISO 216 in 1975, cementing the A series as the global default outside North America. ISO 216’s documented history traces this evolution from a German industrial standard to a near-universal system used in over 190 countries today.

Why Did the United States Not Adopt the A Series?

The United States and Canada continue to use Letter (215.9 by 279.4 millimetres) and Legal size paper instead of A4, largely because these formats were already deeply embedded in American manufacturing, printing, and office equipment before ISO 216 gained international traction. Switching an entire country’s printers, filing cabinets, and paper mills to a new standard proved too costly and disruptive once Letter size was already the entrenched default. This is why documents formatted for A4 sometimes print with slightly cropped margins on American printers set to Letter, and vice versa.

How the A Series Paper Sizes Are Calculated

Understanding the maths behind the A series makes the whole system intuitive rather than something to memorise. The starting point is A0, defined as a rectangle with an area of exactly one square metre and a width to height ratio of 1 to the square root of 2, approximately 1:1.414. This specific ratio is what makes the system self-repeating.

When you cut an A0 sheet exactly in half along its longer edge, you get two rectangles, each with half the area of A0. Because of the square root of two ratio, each of those halves is still proportioned exactly like A0, just smaller. That half-sized rectangle is A1. Cut A1 in half the same way and you get two A2 sheets. Continue the process and you move through A3, A4, A5, all the way down to the tiny A10. Every size in the sequence is precisely half the area of the size before it, and every size shares the identical aspect ratio.

What Do 4A0 and 2A0 Mean If A0 Is the Starting Point?

4A0 and 2A0 sit above A0 in size, which can be confusing since A0 is technically the reference size the whole system is built from. These oversized formats were added later to accommodate very large format printing, and they follow the same doubling logic in reverse. 2A0 is created by doubling A0’s area, and 4A0 by doubling it again, making 4A0 exactly eight times the surface area of A0. Both retain the same aspect ratio as every other A series size.

The Complete Table of Paper Sizes from 4A0 to A10

Below is the full reference table covering every standard A series size, listed with both millimetre and inch dimensions. This table is the one to bookmark for quick lookups when setting up a document template, a plotter job, or a drawing sheet.

Reference table of A series paper sizes from 4A0 to A10, in millimetres and inches

With the full table in front of you, it becomes easier to see the pattern that runs through the whole guide: each row is exactly half the area of the row above it, and the width of one size becomes the height of the next size down. That relationship is what lets drafters, printers, and publishers move between sizes without recalculating proportions from scratch.

Every A Series Paper Size Explained in Detail

Each size in the sequence has its own practical identity, shaped by what fits comfortably on it and what equipment can produce it. Here is what makes each one distinct.

“Halving one sheet’s longer side always produces a smaller sheet with the identical proportions, which is the entire reason the A series can scale from a square metre down to a stamp without distortion.” Structrum Limited — Construction Documentation Standards, 2026

Paper Sizes in Architectural and Construction Drawings in Kenya

Paper size choice on a construction project is not a stylistic decision. It affects whether a drawing is legible at the scale it needs to be read, whether it fits standard drawing registers, and whether a county planning office will accept it. In Kenya, architects and structural engineers preparing drawings for submission to the National Construction Authority and county planning departments typically standardise on A1 for full working drawings and A0 for larger, more complex site or floor layouts, while A3 is common for detail sheets bound into specification documents. A4 remains the default for cover pages, reports, bills of quantities, and correspondence. The full requirements for what a submission needs to include are set out in the building plan submission requirements in Kenya.

Why Does Drawing Scale Depend on Sheet Size?

The relationship between paper size and drawing scale is direct. A building that fits comfortably on an A1 sheet at 1:100 scale would either need to be split across multiple A3 sheets, or drawn at a much smaller and less legible scale, if forced onto A3. This is why larger, more complex buildings default to A0 or A1 sheets, and why an architect’s scope of services in Kenya typically includes decisions about sheet size and layout as part of the technical drawing package, not just the design itself.

How Paper Size Choices Affect Printing and Plotting Costs

Large format sheets like A0 and A1 require a plotter rather than a standard office printer, and printing costs scale with paper area, meaning an A0 sheet costs roughly sixteen times more to print than an A4 sheet of equivalent quality. Kenyan architecture and engineering firms managing large drawing sets often balance this cost against legibility requirements, choosing A1 as a middle ground that keeps drawings readable without the expense of full A0 plots for every sheet in a set.

The B Series and C Series: How They Relate to the A Series

ISO 216 does not stop at the A series. It also defines the B series and, through a related standard, the C series, both of which are built to complement A series sheets rather than replace them.

What Is the B Series Used For?

The B series sits between two consecutive A sizes in area, giving designers an intermediate option when an A size feels too small and the next size up feels excessive. B5, for example, is commonly used for hardcover book printing, sitting between A5 and A4 in area. Passports in many countries, including several using the ISO framework, are sized close to B7.

What Is the C Series Used For?

The C series, defined in ISO 269, exists specifically for envelopes. A C4 envelope is sized to fit an unfolded A4 sheet, a C5 envelope fits an A4 sheet folded once in half, and a C6 envelope fits an A4 sheet folded twice. This is why office stationery suppliers sell A4 paper alongside C4, C5, and C6 envelopes as a matched set.

A Series Paper Sizes Compared to US Letter and Legal Sizes

For anyone working across both systems, the differences are worth knowing precisely. US Letter measures 215.9 by 279.4 millimetres, making it slightly wider and slightly shorter than A4’s 210 by 297 millimetres. US Legal measures 215.9 by 355.6 millimetres, considerably longer than both A4 and Letter, and is mainly used for contracts and legal documents in the United States. Neither Letter nor Legal follows the square root of two ratio that defines the A series, which is why scaling a Letter-formatted document to A4 or vice versa usually shifts the margins slightly rather than fitting perfectly.

How to Choose the Right Paper Size for Your Document or Drawing

Choosing the correct size upfront prevents wasted printing, awkward scaling, and rejected submissions. Here is a structured process for making that choice with confidence.

Common Mistakes to Avoid When Working With A Series Paper Sizes

A few recurring errors show up repeatedly among students and professionals new to the A series system. Knowing them in advance saves reprint costs and formatting headaches.

Confusing Portrait and Landscape Orientation

The A series defines area and proportion, not orientation. An A3 sheet used in landscape orientation is still A3, just rotated. Confusion often arises when a template built for portrait A4 is opened on a landscape A3 plotter setting without adjusting the layout, producing awkward blank space or cropped content.

Assuming All Software Defaults to A4

Many design and word processing programs default to US Letter size out of the box, particularly software developed in the United States. Always confirm the page size setting is switched to A4 or the required drawing sheet size before starting work, rather than after a document is complete.

Scaling a Drawing Without Adjusting Line Weights

Reducing an A1 drawing down to A3 for a bound report shrinks every line, dimension, and text label proportionally. If the original line weights and text sizes were set for A1 legibility, the A3 reduction can become difficult to read. Drafters preparing multi-size drawing sets typically create separate, correctly scaled versions rather than relying on a single reduced print.

Frequently Asked Questions: Paper Sizes from 4A0 to A10