A4 vs US Letter for printable coloring pages

Last updated: 16 September 2026

If you are exporting a coloring page to print, the paper size you pick has to match the paper in the printer. A4 and US Letter look similar on screen and are easy to confuse, but they are different shapes, so a picture sized for one does not fit the other exactly. Here is what actually differs.

The physical difference

	A4	US Letter
Size	210 × 297 mm	8.5 × 11 in
Size in inches	8.268 × 11.693 in	8.5 × 11.0 in
Size in millimetres	210 × 297 mm	215.9 × 279.4 mm
Aspect ratio	1 : 1.4142 (√2)	1 : 1.2941
Area	62,370 mm²	60,322 mm²

Where those numbers come from:

A4 in inches: 210 ÷ 25.4 = 8.2677 in, 297 ÷ 25.4 = 11.6929 in.
US Letter in millimetres: 8.5 × 25.4 = 215.9 mm, 11 × 25.4 = 279.4 mm.
Areas: 210 × 297 = 62,370 mm²; 215.9 × 279.4 = 60,322 mm².
A4 is about 3.4% larger in area: 62,370 ÷ 60,322 = 1.0339.

What that means in practice

A4 is taller and narrower. US Letter is shorter and wider. Because the aspect ratios differ (1.414 against 1.294), a picture drawn to fill one page will not fill the other:

Fitting an A4 page onto US Letter: the height is the binding constraint, so the image is scaled to 279.4 ÷ 297 = 0.941 of its size, leaving side margins.
Fitting a US Letter page onto A4: the width is the binding constraint, so the image is scaled to 210 ÷ 215.9 = 0.973 of its size, leaving top and bottom margins.

Either way you lose a little, so it is worth exporting at the size your printer actually takes rather than letting the printer rescale it at print time.

Pixel dimensions at common DPI

These are the pixel sizes a page has to be to print at a given resolution:

Paper	150 DPI	300 DPI	600 DPI
A4	1240 × 1754	2480 × 3508	4961 × 7016
US Letter	1275 × 1650	2550 × 3300	5100 × 6600

300 DPI is the usual target for something that will be printed and looked at closely. 600 DPI roughly quadruples the file size for a difference most home printers will not show.

Which one should you use

Pick by where the page will be printed, not by preference:

United States and Canada: US Letter is the default paper in virtually every shop and home printer.
Most of the rest of the world: A4 is the default.

If you are making a page for someone else, ask which size their printer takes. If you are making a page to share publicly, exporting both is cheap and removes the guesswork.

Note on sources

A4 dimensions are defined by ISO 216 (210 × 297 mm).
US Letter dimensions are defined by ANSI Y14.1 (8.5 × 11 in).
The 300 DPI pixel values above match what AI Coloring Page Generator exports, which produces both sizes at 300 DPI.
The regional defaults above reflect common practice in those markets, not a formal standard. If you are printing somewhere unusual, check the paper.