Paper Sizes – A, B, C and US Formats
Quick answer: A4 = 210 × 297 mm (21 × 29.7 cm, 8.27 × 11.69 in), A3 = 297 × 420 mm, A5 = 148 × 210 mm, A0 = 841 × 1189 mm ≈ 1 m²; US Letter = 215.9 × 279.4 mm.
Dimensions of A0–A10, B0–B10, C0–C10 envelopes, US Letter, Legal, Tabloid, ANSI and Arch in mm, cm and inches, plus area.
How the calculation works
Choose a format to see its width and height in mm, cm and inches and its area in m² and cm². In reverse, enter dimensions (for example of a measured sheet or drawing) and the calculator finds the nearest standard format, also in landscape.
Formula and assumptions
ISO 216: the aspect ratio is √2 and A0 has an area of 1 m²; each next size is made by halving the longer side (A4 is 1/16 m²). The B series is the geometric mean of neighbouring A sizes and the C series (ISO 269, envelopes) the mean of A and B. US sizes (ANSI/ASME Y14.1) are defined in inches: 1 in = 25.4 mm.
More worked examples
- A4 in cm: 21 × 29.7 cm; area 0.06237 m².
- A3 is a double A4: 29.7 × 42 cm.
- A C4 envelope (229 × 324 mm) takes an unfolded A4 sheet.
- US Letter 8.5 × 11 in = 21.59 × 27.94 cm.
A series sizes (ISO 216)
| Size | mm | cm |
|---|---|---|
| A0 | 841 × 1189 | 84.1 × 118.9 |
| A1 | 594 × 841 | 59.4 × 84.1 |
| A2 | 420 × 594 | 42 × 59.4 |
| A3 | 297 × 420 | 29.7 × 42 |
| A4 | 210 × 297 | 21 × 29.7 |
| A5 | 148 × 210 | 14.8 × 21 |
| A6 | 105 × 148 | 10.5 × 14.8 |
Common mistakes
- Confusing US Letter with A4 – Letter is 6 mm wider and 18 mm shorter.
- Assuming the B series is smaller than A – B4 is larger than A4.
- Rounding to whole centimetres (A4 is not 21 × 30 cm).
Frequently asked questions
What are the dimensions of A4 in cm?
A4 is 21 × 29.7 cm (210 × 297 mm), or 8.27 × 11.69 inches.
How big is A3?
A3 is 297 × 420 mm (29.7 × 42 cm), twice the size of A4.
How many A4 sheets fit in A0?
A0 (1 m²) holds 16 A4 sheets; A1 holds 8, A2 4 and A3 2.
What is the difference between A4 and Letter?
Letter is 215.9 × 279.4 mm, A4 is 210 × 297 mm – Letter is wider and shorter.
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