Paper Size Converter
Give exact A, B, and C series dimensions in millimeters, inches, and area.
Get exact paper dimensions instantly. Free A, B, C series paper size converter with mm, inches and area.
Calculator Inputs
About Paper Sizes
Give exact A, B, and C series dimensions in millimeters, inches, and area.
The ISO system starts each series at nought and halves the long side each step, keeping the √2 aspect ratio forever: A4 is just A0 halved four times. B sizes sit geometrically between A sizes for posters; C sizes fit A sheets as envelopes (a C4 envelope holds an A4 sheet).
US Letter (8.5×11 in) is close to — but not — A4 (210×297 mm); designs must be adapted, not just printed. Everything runs in your browser.
Where it is used
Print setup, envelope matching (C fits A), poster sizing, and checking US Letter vs A4.
How to use the Paper Sizes
- Series — enter the value.
- Size Number (0–10) — enter the value (e.g. 4).
- Calculate — press the Calculate button to see the result instantly above.
Formula
Halve the long side per step (floor mm); A0 = 841×1189 (1 m²).
Examples
Example
Frequently Asked Questions
- Why does halving keep the same shape?
- The √2:1 ratio is the unique rectangle that, halved across the long side, yields two rectangles of identical proportions.
- Which envelope fits A4?
- C4. The C series is sized so each envelope comfortably holds its A-series sheet (C4 ≈ 229×324 mm vs A4 210×297 mm).
- Is US Letter the same as A4?
- No. Letter is 215.9×279.4 mm — wider but shorter than A4’s 210×297 mm. Never assume interchangeability in print files.