About the Paper Size Converter
This paper size converter gives the exact dimensions of every common sheet — ISO A0–A10, B0–B10 and C0–C10, plus US Letter, Legal, Tabloid, ANSI and architectural sizes — in millimetres, inches, PostScript points and pixels at the resolution you choose. Pick a size and orientation and you have everything needed to set up a document, a print file or a scanner.
Designers use it to size artwork at 300 DPI for print, office workers to understand why an A4 file prints with cut-off margins on Letter paper, and anyone sending documents between Europe and North America to pick the right scale. The “scale to fit” result tells you the print zoom that fits one size entirely onto another without cropping.
ISO A and B sizes come from ISO 216 and C envelope sizes from ISO 269: each size has a 1 : √2 aspect ratio and halves into the next. US sizes are defined in inches and converted at exactly 25.4 mm per inch; pixel dimensions are rounded to the nearest whole pixel.
How to use the paper size converter
- 1Choose a paper size from the A, B, C, US, ANSI or Arch list.
- 2Pick portrait or landscape orientation.
- 3Enter the resolution you will print or export at (300 DPI for quality print).
- 4Choose a second size to see the scale needed to fit one onto the other.
- 5Copy the dimensions or pixel size into your document or image editor.
Formula and method
ISO sizes are defined in whole millimetres. A0 has an area of one square metre with sides in the ratio 1 : √2, and each following size is made by halving the longer side (A4 = 210 × 297 mm). B sizes are the geometric means between A sizes, and C envelope sizes sit between A and B so an A4 sheet slips into a C4 envelope.
US sizes are defined in inches; 1 inch is exactly 25.4 mm and 72 PostScript points. Pixel dimensions multiply inches by the DPI and round to whole pixels. The scale to fit compares both sheets in the same orientation and uses the smaller of the width and height ratios, so the whole page fits without cropping.
- DPI
- Dots (pixels) per inch
- W₁, H₁
- Width and height of the selected size
- W₂, H₂
- Width and height of the size you scale onto
Worked examples
A4 at 300 DPI, printed on US Letter
A4 is 210 × 297 mm, or 8.27 × 11.69 in. At 300 DPI that is 2,480 × 3,508 pixels. Letter is wider but shorter (215.9 × 279.4 mm), so fitting an A4 page onto Letter needs 279.4 ÷ 297 = 94.1% scale.
US Letter landscape at 150 DPI, fitted to A4
Letter is 8.5 × 11 in; in landscape it is 11 × 8.5 in (279.4 × 215.9 mm), which is 1,650 × 1,275 pixels at 150 DPI. A4 landscape is only 210 mm tall, so the page must shrink to 210 ÷ 215.9 = 97.3% to fit.
A3 poster at 72 DPI, scaled down to A4
A3 is 297 × 420 mm (11.69 × 16.54 in), or 842 × 1,191 px at 72 DPI. Because each A size is half the one above, A3 shrinks to A4 at 1/√2 ≈ 70.7%.
Frequently asked questions
What is A4 size in inches?+
A4 is 210 × 297 mm, which is 8.27 × 11.69 inches. It is slightly narrower and about 0.7 in taller than US Letter (8.5 × 11 in).
What is the difference between Letter and A4?+
Letter (8.5 × 11 in, 215.9 × 279.4 mm) is used in the US, Canada and parts of Latin America. A4 (210 × 297 mm) is the standard almost everywhere else. Printing one on the other needs about 94–97% scaling to avoid cropping.
How many pixels is A4 at 300 DPI?+
A4 at 300 DPI is 2,480 × 3,508 pixels (about 8.7 megapixels). At 150 DPI it is 1,240 × 1,754 px, and at 72 DPI it is 595 × 842 px.
Why do A sizes have a 1 : √2 ratio?+
With a 1 : √2 ratio, cutting a sheet in half across its long side gives two sheets of the same shape. That is why A3 halves to A4, and why enlarging A4 to A3 on a copier uses 141%.
Which envelope fits an A4 sheet?+
A C4 envelope (229 × 324 mm) fits an unfolded A4 sheet, C5 fits A4 folded in half once (A5), C6 fits A4 folded in half twice (A6), and a DL envelope (110 × 220 mm) fits A4 folded into thirds.