Unit & Measurement Tables
Paper Size Table
The A series works on one idea: every size has the same shape, and folding it in half gives the next size down. For that to be true the long side must be √2 times the short side, because halving the long side turns the sheet sideways and reproduces the same ratio. A0 is defined as one square metre of that shape, which fixes every other size.
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The practical consequence is that A4 is exactly one sixteenth of A0, A3 is one eighth, and sixteen A4 pages tile an A0 poster with no gaps. That is why the system survives in printing, where every other unit has been metricated: the ratio does the work that a formula would otherwise have to do.
The B series is the geometric mean between successive A sizes — B4 sits between A4 and A3, slightly larger than A4. The C series exists only for envelopes and is sized so that an A sheet fits inside the matching C envelope with a few millimetres to spare: A4 goes flat into C4, folded twice into C6.
North America never adopted the system. US Letter is 216 × 279 mm, close enough to A4 that people assume they are the same, but 6 mm narrower and 18 mm taller. A document designed for one will reflow when printed on the other, which is why print dialogs offer a scale-to-fit option. The last table gives both so the difference is visible rather than assumed.
ISO 216 A series
| Size | Width × height (mm) | Width × height (in) | Area (m²) | Pixels at 300 dpi |
|---|---|---|---|---|
| A0 | 841 × 1189 | 33.11 × 46.81 | 0.9999 | 9,933 × 14,043 |
| A1 | 594 × 841 | 23.39 × 33.11 | 0.4996 | 7,016 × 9,933 |
| A2 | 420 × 594 | 16.54 × 23.39 | 0.2495 | 4,961 × 7,016 |
| A3 | 297 × 420 | 11.69 × 16.54 | 0.1247 | 3,508 × 4,961 |
| A4 | 210 × 297 | 8.27 × 11.69 | 0.0624 | 2,480 × 3,508 |
| A5 | 148 × 210 | 5.83 × 8.27 | 0.0311 | 1,748 × 2,480 |
| A6 | 105 × 148 | 4.13 × 5.83 | 0.0155 | 1,240 × 1,748 |
| A7 | 74 × 105 | 2.91 × 4.13 | 0.0078 | 874 × 1,240 |
| A8 | 52 × 74 | 2.05 × 2.91 | 0.0038 | 614 × 874 |
| A9 | 37 × 52 | 1.46 × 2.05 | 0.0019 | 437 × 614 |
| A10 | 26 × 37 | 1.02 × 1.46 | 0.0010 | 307 × 437 |
A0 is one square metre by definition. Each step halves the area: A4 is one sixteenth of A0, which is why 16 pages of A4 make an A0 poster.
ISO 216 B series
| Size | Width × height (mm) | Width × height (in) | Area (m²) | Pixels at 300 dpi |
|---|---|---|---|---|
| B0 | 1000 × 1414 | 39.37 × 55.67 | 1.4140 | 11,811 × 16,701 |
| B1 | 707 × 1000 | 27.83 × 39.37 | 0.7070 | 8,350 × 11,811 |
| B2 | 500 × 707 | 19.69 × 27.83 | 0.3535 | 5,906 × 8,350 |
| B3 | 353 × 500 | 13.90 × 19.69 | 0.1765 | 4,169 × 5,906 |
| B4 | 250 × 353 | 9.84 × 13.90 | 0.0883 | 2,953 × 4,169 |
| B5 | 176 × 250 | 6.93 × 9.84 | 0.0440 | 2,079 × 2,953 |
| B6 | 125 × 176 | 4.92 × 6.93 | 0.0220 | 1,476 × 2,079 |
| B7 | 88 × 125 | 3.46 × 4.92 | 0.0110 | 1,039 × 1,476 |
| B8 | 62 × 88 | 2.44 × 3.46 | 0.0055 | 732 × 1,039 |
| B9 | 44 × 62 | 1.73 × 2.44 | 0.0027 | 520 × 732 |
| B10 | 31 × 44 | 1.22 × 1.73 | 0.0014 | 366 × 520 |
B series sheets sit between the A sizes: B4 is larger than A4 and smaller than A3. B5 is the common book size in much of Europe and Japan.
ISO 269 C series (envelopes)
| Size | Width × height (mm) | Width × height (in) | Area (m²) | Pixels at 300 dpi |
|---|---|---|---|---|
| C0 | 917 × 1297 | 36.10 × 51.06 | 1.1893 | 10,831 × 15,319 |
| C1 | 648 × 917 | 25.51 × 36.10 | 0.5942 | 7,654 × 10,831 |
| C2 | 458 × 648 | 18.03 × 25.51 | 0.2968 | 5,409 × 7,654 |
| C3 | 324 × 458 | 12.76 × 18.03 | 0.1484 | 3,827 × 5,409 |
| C4 | 229 × 324 | 9.02 × 12.76 | 0.0742 | 2,705 × 3,827 |
| C5 | 162 × 229 | 6.38 × 9.02 | 0.0371 | 1,913 × 2,705 |
| C6 | 114 × 162 | 4.49 × 6.38 | 0.0185 | 1,346 × 1,913 |
| C7 | 81 × 114 | 3.19 × 4.49 | 0.0092 | 957 × 1,346 |
| C8 | 57 × 81 | 2.24 × 3.19 | 0.0046 | 673 × 957 |
C sizes are built for envelopes: a C4 envelope holds an A4 sheet flat, and a C6 envelope holds an A4 sheet folded into quarters.
North American paper sizes
| Size | Width × height (in) | Width × height (mm) | Area (in²) | Pixels at 300 dpi |
|---|---|---|---|---|
| Letter | 8.50 × 11.00 | 215.9 × 279.4 | 93.50 | 2,550 × 3,300 |
| Legal | 8.50 × 14.00 | 215.9 × 355.6 | 119.00 | 2,550 × 4,200 |
| Tabloid | 11.00 × 17.00 | 279.4 × 431.8 | 187.00 | 3,300 × 5,100 |
| Ledger | 17.00 × 11.00 | 431.8 × 279.4 | 187.00 | 5,100 × 3,300 |
| Executive | 7.25 × 10.50 | 184.1 × 266.7 | 76.13 | 2,175 × 3,150 |
| Half Letter | 5.50 × 8.50 | 139.7 × 215.9 | 46.75 | 1,650 × 2,550 |
| Junior Legal | 5.00 × 8.00 | 127.0 × 203.2 | 40.00 | 1,500 × 2,400 |
| Government Letter | 8.00 × 10.50 | 203.2 × 266.7 | 84.00 | 2,400 × 3,150 |
US Letter is 216 × 279 mm, close to A4 but not interchangeable: A4 is 6 mm narrower and 18 mm taller, so a document laid out for one reflows on the other.
How to Use These Tables
- Choosing a poster: A0 is 841 × 1189 mm, which is sixteen A4 sheets. A1 is eight, A2 is four, and A3 is two.
- Preparing a print file: at 300 dpi an A4 page needs 2480 × 3508 pixels. At 150 dpi the same page is 1240 × 1754, and at 72 dpi it is 595 × 842.
- Buying envelopes: match the letter to the C size. A4 flat needs C4, A4 folded once needs C5, A4 folded in quarters needs C6, and A5 flat needs C5.
- Fitting US content on European paper: scale US Letter to 97% to fit A4 width, or accept the reflow. Legal is 216 × 356 mm and has no ISO equivalent.
- Checking a book: B5 (176 × 250 mm) and A5 (148 × 210 mm) are the two common trade paperback sizes, and B5 is noticeably larger.
Common Questions
Why is A4 exactly 210 by 297 millimetres?
Because A0 is defined as one square metre with a √2 aspect ratio, and each size is the previous one halved and rounded to the nearest millimetre. The rounding is part of the standard, so the numbers are definitions rather than calculations.
Is US Letter the same as A4?
No. Letter is 216 × 279 mm and A4 is 210 × 297 mm. A4 is 6 mm narrower and 18 mm taller, so a Letter document printed on A4 reflows, and an A4 document on Letter gets scaled to about 97%.
How many A4 pages fit on A0?
Sixteen. Each step in the series halves the area, so A0 = 2 × A1 = 4 × A2 = 8 × A3 = 16 × A4. This is why A0 posters are assembled from A4 tiles.
What is the B series for?
B sizes are the geometric mean between neighbouring A sizes, so B4 is larger than A4 and smaller than A3. They are used for books, posters and envelopes where an A size is slightly too small.
Which envelope fits an A4 sheet?
C4 for a flat A4, C5 for A4 folded once, and C6 for A4 folded into quarters. The C series is defined so the matching A size fits with a small margin.
How many pixels is A4 at 300 dpi?
2480 × 3508. Multiply the millimetre size by 300 and divide by 25.4. At 150 dpi it halves to 1240 × 1754, and at 72 dpi it is 595 × 842.
More Unit & Measurement Tables
Sources
- ISO 216 — Writing paper and certain classes of printed matter, trimmed sizes — International Organization for Standardization
- ISO 269 — Correspondence envelopes, designation and sizes — International Organization for Standardization
- ANSI/ASME Y14.1 — Decimal inch drawing sheet size and format — American National Standards Institute
Filed with Unit Conversion calculations.