Paper Size Converter (A4, Letter, ANSI, ARCH, and Pixels)

Every ISO 216 A, B and C size, the DIN overformats, and the North American named, ANSI and ARCH sheets — in millimetres, centimetres, inches, points and pixels at whatever resolution you are working at. The ISO sizes are constructed from the standard’s own halving rule rather than copied from its table.

One base pair, then halve and round down

The whole of ISO 216, constructed from three base pairs

North American sizes: named, ANSI and ARCH

Pixel dimensions at five working resolutions

A series you can compute, and a series you have to look up

ISO 216 is the rare standard you do not need a copy of. It fixes A0 at 841 × 1189 mm and then defines every other A size by one rule: halve the long side and round down to the whole millimetre. Apply it four times and you get A4 = 210 × 297 mm, which is the published size exactly. Apply it ten times and you get A10 = 26 × 37, also exact. The B series starts from a short side of exactly one metre, B0 = 1000 × 1414, and the C series — the envelopes — from C0 = 917 × 1297, each C size being the geometric mean of the A and B sizes of the same number. That is why a C4 envelope swallows an A4 sheet and a B4 sheet swallows the C4.

The rounding rule is doing real work, and it has one trap. The exact geometry of A0 — a square metre at an aspect of √2 — is 840.896 × 1189.207 mm, and the published 841 × 1189 is that rounded to the nearest millimetre, not down. C0’s exact long side is 1296.84 mm and the published figure is 1297, rounded up again. So you cannot generate the series by flooring the exact geometry: you have to start from the base pairs the standard states and floor from there. Do that and the halving rule and the closed form ⌊base ÷ 2^n/2⌋ agree at every one of the thirty-three published sizes, and on out to n = 20. The B series, which might have been expected to misbehave because it is defined by geometric means rather than halving, behaves perfectly: B0’s exact long side of 1414.214 mm floors to the published 1414.

The North American sizes are the opposite kind of thing. Letter, Legal, Tabloid, the ANSI A to E engineering sheets and the ARCH architectural sheets are trade conventions with no geometric relationship, so they are a table and this page treats them as one. The cost of that shows in one row: because ANSI’s aspect ratio is arbitrary, the series alternates between 1.294 and 1.545, and halving an ANSI sheet does not give you the next ANSI sheet. The ARCH series is a little better behaved at 4:3 and 3:2, but no standards body appears to define it at all — ANSI/ASME Y14.1 covers ANSI A to E and stops.

US Letter and A4 are not interchangeable, and the difference is not small. A4 is 210 × 297 mm; Letter is 215.9 × 279.4. A4 is 5.9 mm narrower and 17.6 mm taller, so neither contains the other and there is no orientation in which one substitutes for the other. What “fit to page” then does is scale the whole document by 94.07% to get A4 onto Letter, or by 97.3% the other way — and because that scale is applied to both axes it moves your type size, your margins and your line spacing together. An 11 pt document printed “fit to page” from A4 onto Letter is set in 10.35 pt. This is why a document that has to print correctly in both places is laid out to the intersection: 210 mm wide by 279 mm tall, with margins that absorb the rest.

And the pixel answer, which is the reason this page exists. A paper size has no pixel dimensions until you choose a resolution, so there is nothing to look up: A4 is 2,480 × 3,508 px at 300 dpi, 1,240 × 1,754 at 150, and 794 × 1,123 at 96, which is the CSS reference resolution. If you are choosing that number rather than being handed it, the DPI and print size calculator works out which resolution the job actually needs, and the typographic units converter handles the points and picas a page box is specified in. The figures behind this conversion come from a published table, not a definition, so a different source may give slightly different numbers. The reference below is the one used here.

Frequently asked questions

Related calculators

References

1. ISO 216:2007, Writing paper and certain classes of printed matter — Trimmed sizes — A and B series, and indication of machine direction. Copyrighted; no table from it is reproduced here and none is needed. What this page uses is its prose construction, as summarised in Wikipedia’s ISO 216 article (read 26 September 2026): A0 is 841 × 1189 mm, “each successive size … can be cut by halving the length of the preceding size sheet” and “the new measurement is rounded down to the nearest millimetre”; the B series places geometric means between adjacent A sizes with B0’s short side exactly 1 m; the C series are the geometric means of the A and B sizes of the same number. The tolerances quoted are also from that article: ±1.5 mm up to 150 mm, ±2.0 mm from 150 to 600 mm, ±3.0 mm above.
2. ANSI/ASME Y14.1, Decimal Inch Drawing Sheet Size and Format, the source of ANSI A to E. Copyrighted; the five sizes are cited from Wikipedia’s ANSI/ASME Y14.1 article (read 26 September 2026), which also makes the point this page repeats: because the aspect ratio is arbitrary, the series “has two alternating aspect ratios”, 22/17 and 17/11.
3. Archtoolbox, Standard Paper Sizes (archtoolbox.com/paper-sizes/, read 26 September 2026), for the ARCH series: ARCH A 9 × 12, B 12 × 18, C 18 × 24, D 24 × 36, E1 30 × 42, E 36 × 48 inches. The ARCH sizes are a North American drawing-office convention rather than a published standard, and no standards body could be found that defines them; that is stated on the page.
4. papersizes.org, US Paper Sizes, and papersizes.io, US (both read 26 September 2026), used as the two sources the North American table is cross-checked between. They agree on Letter, Legal, Junior Legal, Half Letter, Tabloid/Ledger and the ANSI and ARCH series, and they disagree on Government Letter (8 × 10 against 8 × 10½), which is therefore left off.
5. letterformat.org, Executive Paper Size Details (read 26 September 2026), giving Executive as 7¼ × 10½ in (184 × 267 mm). Engineering ToolBox’s office-paper table prints “7 × 10” in its inch column beside 184.2 × 266.7 mm in its metric one, which are not the same sheet; the metric figures agree with 7¼ × 10½ and that is the pair used here.
6. National Institute of Standards and Technology, Refinement of Values for the Yard and the Pound, Federal Register notice of 1 July 1959, which fixed the international inch at exactly 25.4 mm and the avoirdupois pound at exactly 0.45359237 kg. Both exact values are used throughout this batch; every inch-to-millimetre figure here is therefore exact, not approximate.
7. W3C, CSS Values and Units Module Level 4 (w3.org/TR/css-values-4/ and the editor’s draft at drafts.csswg.org, read 26 September 2026) — a public specification, quoted directly. It fixes 1in = 96px, 1pt = 1/72in, 1pc = 12pt and 1px = 1/96in; defines em as “the computed value of the font-size property of the element on which it is used”, and notes that in the font-size property itself it resolves against the size inherited from the parent; defines rem as “the computed value of the em unit on the root element”; and defines ex as the used x-height and ch as the advance measure of the “0” glyph — both font metrics, which is why this page refuses them. It also gives the fallbacks the spec mandates when those metrics are unavailable: “a value of 0.5em must be assumed” for ex.