Editorial Process
Each dimension on this site traces to a published standard or an official postal or trade specification. This page names each source, separates the values that are defined from the ones we calculate, and states how a correction is made.
Sources We Cite
| Standard | Governs | Applies to | Edition | Last checked |
|---|---|---|---|---|
| ISO 216 | Trimmed sizes of writing paper and printed matter | A series, B series | 2007 | 2026-09-01 |
| ISO 269 | Correspondence envelope sizes | C series, DL | 1985 † | 2026-09-01 |
| ISO 217 | Untrimmed stock sizes | RA, SRA | 2013 | 2026-09-01 |
| ISO 536 | Paper and board, grammage | GSM values | 2019 | 2026-09-01 |
| ASME Y14.1 | US drawing sheet sizes | ANSI A-E | 2020 | 2026-09-01 |
| USPS DMM 201 | US mailpiece dimension limits | Letter, postcard, flat limits | 2026 | 2026-09-01 |
| JIS P 0138 | Japanese paper sizes | JIS B series, A series | 2011 | 2026-09-01 |
| Wikipedia, International standard paper sizes | Secondary cross-check for the defining formulas, history and country adoption | context | , | 2026-09-02 |
| DIN 476 | Historical origin of the ISO A/B system | context only | 1922 | , |
† ISO 269 was withdrawn in 2009 without a direct replacement. C-series envelope sizes are still defined by it in practice, so it stays on the list with that note.
Defined Values, and Calculated Ones
Defined values come straight from the standard. For an ISO size that means the portrait millimetre width and height, rounded the way the standard rounds them. Everything else is calculated from those millimetres by a fixed formula and is never copied from another site.
- Centimetres = mm ÷ 10
- Inches = mm ÷ 25.4
- Points = mm ÷ 25.4 × 72
- Picas = points ÷ 12
- Pixels = mm ÷ 25.4 × DPI
- Area = width × height
- Diagonal = √(width² + height²)
- Aspect ratio = height ÷ width
Rounding: two decimals for centimetres and inches, whole numbers for pixels, one decimal for picas. The unrounded figure stays in the dataset.
How a Number Becomes a Page
- Pulled from the official text of the governing standard.
- Cross-checked against a second authority: a national standards body, a postal operator’s spec, a manufacturer’s data sheet, or the ISO catalogue entry itself.
- Computed, derived values run through the formulas above and are spot-checked by hand.
- Dated with the day it was verified.
- Read end to end by an editor, against a sibling page, before it publishes.
When a Value Is Wrong
It is fixed at the source dataset and the page redeploys the same day. A material change is logged with its date on the affected page’s provenance line.
Freshness
Physical paper standards move slowly, ISO 216 has held since 1975. Screen and social-media specs change often, so those pages carry a visible last-verified date and are re-checked on a schedule.
✓ This page is reviewed on a schedule. Last reviewed . Editorial Process →