Paper Size Converter
Look up the exact dimensions of any standard paper size — ISO A, B and C series plus North American Letter, Legal, Tabloid and Ledger — in millimetres, centimetres, inches and pixels at common print resolutions. Useful when you are setting up a document, exporting artwork at the right pixel dimensions, or checking whether a design will fit a given sheet. The pixel sizes update for 72, 96, 150 and 300 DPI.
How to use this tool
- Choose a paper size from the list — A4, Letter and other common sizes are near the top.
- Read its width and height in millimetres, centimetres and inches.
- Check the pixel dimensions at 72, 96, 150 and 300 DPI for on-screen and print work.
- Use 300 DPI pixel sizes when exporting artwork for print, and 96 DPI for typical screen work.
- Copy the summary to paste into a document setup or design brief.
The formula
ISO sizes follow a rule: every sheet has sides in the ratio 1 : √2, and each size is half the previous one. Pixel dimensions come from the physical size and the chosen resolution.
aspect ratio = 1 : √2 (≈ 1.414) for all ISO sizes
A(n+1) = half of A(n)
pixels = inches × DPI = (mm ÷ 25.4) × DPI- √2
- The ratio of long to short side, preserved when halved
- DPI
- Dots per inch — print/screen resolution
The √2 ratio is why scaling a document from A4 to A3 (or two-up on A4) never leaves margins: the proportions are identical at every size.
Worked examples
A4 for print
- Given
- A4 at 300 DPI
- Result
- 2480 × 3508 px
A4 is 210 × 297 mm, which at 300 dots per inch is 2480 × 3508 pixels — the standard print export size.
US Letter
- Given
- Letter size
- Result
- 8.5 × 11 in / 216 × 279 mm
Letter is defined in inches; the tool also gives its millimetre equivalent for comparison with A4.
Halving the series
- Given
- A3 folded to A4
- Result
- A4 is exactly half of A3
Because ISO sizes share the √2 ratio, folding A3 in half gives two A4 sheets with no wasted paper.
Frequently asked questions
A4 comes from the ISO 216 system, which starts with A0 at exactly one square metre and a 1 : √2 side ratio, then halves down. A4 is A0 halved four times, giving 210 × 297 mm. The clever ratio means every size keeps the same proportions when halved.
A4 (210 × 297 mm) is a little narrower and taller than US Letter (216 × 279 mm). They are close but not interchangeable: a document laid out for one can clip or leave odd margins on the other, so set your page size to match your intended paper.
Use 300 DPI for print-quality artwork, 150 DPI for draft prints, and 96 DPI (or 72 for legacy work) for on-screen use. Higher DPI means more pixels and a sharper print, but larger files. The tool shows all four so you can pick the right one.
The B series sits between A sizes and is used for posters, books and envelopes that need to be a bit larger. The C series is sized for envelopes that hold A-series sheets — a C4 envelope fits an unfolded A4 sheet, and C5 fits A4 folded once.
The ISO sizes are exact by definition, rounded to the millimetre as the standard specifies. The US sizes are exact in inches. Pixel values are rounded to the nearest whole pixel, which is all a raster image can be.
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