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Paper Sizes Explained

Moleskine Notebook

Paper sizes are an unfortunately confusing thing. You just want some printer paper or a notebook and instead you are choosing between “A4” and “B5” and other unhelpful options. Maybe you are better off when switching to numbers, like “8.5 by 11” but we’ve all made the mistake of ordering legal paper when we meant to get normal.

This guide should help you sort out all your paper size problems.

Paper Size Standards

A4, A6, and so on are not sizes that were arrived a randomly, they are the result of ISO standard 216. ISO 216 defines paper sizes in the “A” and “B” series with ISO 217 and ISO 269 (specifically the “C” series) standards handling related products, like envelopes.

ISO vs. US

In the United States it’s common to see sizes like A4, but paper is more commonly referred to as “Letter,” “Legal,” “Memo” or terms like that. This is because the US standard is based on ANSI (American National Standards Institute) standards, which are different from ISO. These names are actually not the official names, but rather shorthand for the ANSI name.

The main paper sizes in the US standards are:

  • Legal: 8 1⁄2 x 14 inches / 216 x 356 mm
  • Letter (ANSI A): 8 1⁄2 x 12 2⁄3 inches / 216 x 322 mm
  • Government Letter: 8 x 10 inches / 203 x 254 mm

The specific standard here is known as ANSI/ASME Y14.1.

Understanding Paper Size Naming

The names themselves are quite simple: you have a series name and then a size name. In the ISO standard these combine to make “A4” or “B6”. The challenge here is remembering what those sizes mean and how big they are relative to one another.

The most important rule to remember is that the numbers are in inverse order, so size 0 paper is larger than size 5.

A Series Paper Sizes

The most common paper sizes are part of the “A” series, which contains commonly referred to types of loose paper, like “printer paper” and “legal paper.” These names are often shorthand that are used to refer to standard sizes, but they can also refer to ANSI sizes, so you have to be careful what you ask for!

  • A0: 841 x 1189 mm / 33 1⁄8 x 46 19⁄24 inches
  • A1: 594 x 841 mm / 23 3⁄8 x 33 1⁄8 inches
  • A2: 420 x 594 mm / 16 13⁄24 x 23 3⁄8 inches
  • A3: 297 x 420 mm / 11 17⁄24 x 16 13⁄24 inches
  • A4: 210 x 297 mm / 8 1⁄4 x 11 17⁄24 inches
  • A5: 148 x 210 mm / 5 5⁄6 x 8 1⁄4 inches
  • A6: 105 x 148 mm / 4 1⁄8 x 5 5⁄6 inches
  • A7: 74 x 105 mm / 2 11⁄12 x 4 1⁄8 inches
  • A8: 52 x 74 mm / 2 1⁄24 x 2 11⁄12 inches
  • A9: 37 x 52 mm / 1 11⁄24 x 2 1⁄24 inches
  • A10: 26 x 37 mm / 1 1⁄24 x 1 11⁄24 inches

B Series Paper Sizes

These are paper sizes that are different from A series sizes, but not necessarily smaller or larger. B sizes might just seem like weird sizes, but they can be quite useful if you can get your head around the range.

  • B0: 1000 x 1414 mm / 39 3⁄8 x 55 2⁄3 inches
  • B1: 707 x 1000 mm / 27 5⁄6 x 39 3⁄8 inches
  • B2: 514 x 728 mm / 19 2⁄3 x 27 5⁄6 inches
  • B3: 364 x 514 mm / 13 11⁄12 x 19 2⁄3 inches
  • B4: 257 x 364 mm / 9 5⁄6 x 13 11⁄12 inches
  • B5: 182 x 257 mm / 6 11⁄12 x 9 5⁄6 inches
  • B6: 128 x 182 mm / 4 11⁄12 x 6 11⁄12 inches
  • B7: 88 x 125 mm / 3 11⁄24 x 4 11⁄12 inches
  • B8: 62 x 88 mm /  2 11⁄24 x 3 11⁄24 inches
  • B9: 44 x 62 mm / 1 3⁄4 x 2 11⁄24 inches
  • B10: 31 x 44 mm / 1 5⁄24 x 1 3⁄4 inches

C Series Paper Sizes

These are the ISO standards for envelopes and other related paper products.

  • C0: 917 x 1,297 mm / 36 1⁄12 x 51 1⁄12 inches
  • C1: 648 x 917 mm / 25 1⁄2 x 36 1⁄12 inches
  • C2: 458 x 648 mm / 18 1⁄24 x 25 1⁄2 inches
  • C3: 324 x 458 mm / 12 3⁄4 x 18 1⁄24 inches
  • C4: 229 x 324 mm / 9 x 12 3⁄4 inches
  • C5: 162 x 229 mm / 6 3⁄8 x 9 inches
  • C6: 114 x 162 mm / 4 1⁄2 x 6 3⁄8 inches
  • C7: 81 x 114 mm / 3 5⁄24 x 4 1⁄2 inches
  • C8: 57 x 81 mm / 2 1⁄4 x 3 5⁄24 inches
  • C9: 40 x 57 mm / 1 7⁄12 x 2 1⁄4 inches
  • C10: 28 x 40 mm / 1 1⁄12 x 1 7⁄12 inches

Other Paper Sizes

Keep in mind that there are many other paper sizes as well. First of all, paper doesn’t have to adhere to a standard at all. Paper and notebook papers are free to create product that is any size they want! That said it can be prohibitively expensive to create paper in custom sizes and this can be difficult to do at scale.

There are also standard sizes that are quite rare. These include huge sizes like 4A0, which is an enormous 1682 x 2378 mm (about 5 by 7 feet), and 2A0 which is 1189 x 1682 mm.

There are other sizes that are variants on the mainline sizes. These come in sizes like “A4 extra” (235 x 322 mm / 9.25 x 12.67 inches) and “A4 Super” (229 x 322 mm / 9.25 x 12.67 inches).

Frequently Asked Questions

What is a standard printer paper size?

Standard printer paper in the United State and Canada is called “letter” paper as per the ANSI standard. It’s sized at 8.5 x 11 inches. Other parts of the world use A4 as their standard printer paper, which is 210 x 297 mm (8 1⁄4 x 11 17⁄24 inches).

What is a standard envelop size?

Normal North American business envelopes are size #10. They measure 4 1/8 by 9 1/2 inches.

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