# Paper Sizes

Did you know that international paper sizes (like A3, A4, etc) are based on the square root of 2?

Because the square root of 2 has this cool property:

1 × √2 × √2 = 2

Which lets us have this: So we can have sheets that have exactly the same proportions (their ratio of side lengths are the same) and also fit in each other perfectly: Two A4s make an A3
and have the same proportions

This makes things really efficient:

• Don't have any A3? Tape two A4's together.
• Don't have any A5? Cut an A4 in half.

And because they have the same proportions, any artwork or document can be resized to fit on any sheet: Another benefit is that you can print something out at 70% size and fit 2 pages side-by-side on just one sheet like this: Why 70%? Because 1/√2 = 0.7071... which is close to 70%

A similar enlargement is √2 = 1.4142... which is close to 140%

## Sizes

The popular A4 size is 210 mm wide by 297 mm high: With a width of 210 the height is: 210 × √2 ≈ 297

Here are all the sizes cut from an A0 sheet (which has an area of 1.0 m2): Lastly here are the official sizes:

size mm × mm about the size of a   area
A0 841 × 1189 table top   1.0 m2
A1 594 × 841     0.5 m2
A2 420 × 594 monitor   0.25 m2
A3 297 × 420     0.125 m2
A4 210 × 297 writing sheet   0.0624 m2
A5 148 × 210     0.0311 m2
A6 105 × 148     0.0155 m2
A7 74 × 105 note   0.00777 m2
A8 52 × 74     0.003848 m2
A9 37 × 52     0.001924 m2
A10 26 × 37 stamp   0.000962 m2

Note: you can think of the "A-number" as how many folds (or cuts-in-half) away from an A0 we are. So an A3 needs 3 folds of an A0, and so is ½×½×½ = 1/8th the size.