A4 Paper Size in Pixels at 72, 96, 150 and 300 DPI

The short answer

A4 paper is 210 × 297 mm, which is 8.27 × 11.69 in. Its size in pixels depends entirely on the resolution you choose:

A sheet of paper has no pixels of its own. "A4 in pixels" only makes sense once you attach a DPI (dots, or pixels, per inch) that says how many pixels represent one inch of paper.

Where the A series comes from

ISO 216 defines the A series with two rules. First, A0 has an area of exactly one square meter. Second, every sheet has an aspect ratio of 1 : √2, roughly 1 : 1.414. Those two conditions give A0 a size of 841 × 1189 mm.

Each smaller size is made by cutting the sheet in half across its long edge: A1 is 594 × 841 mm, A2 is 420 × 594 mm, A3 is 297 × 420 mm, A4 is 210 × 297 mm, and A5 is 148 × 210 mm. Because the ratio is √2, the halves keep the same proportions as the original, which is why an A4 document scales cleanly onto A3 or A5. Check the ratio for A4: 297 / 210 ≈ 1.4143, within rounding of √2.

The formula

Converting any paper size to pixels takes two steps: turn millimeters into inches, then multiply by the resolution.

pixels = (millimeters / 25.4) × DPI

For A4 at 300 DPI:

• Width: 210 / 25.4 = 8.2677 in; 8.2677 × 300 = 2480.3 → 2480 px
• Height: 297 / 25.4 = 11.6929 in; 11.6929 × 300 = 3507.9 → 3508 px

The results are rounded to whole pixels, so a document that is exactly 2480 × 3508 px is a hair over 210 × 297 mm at 300 DPI.

The same formula gives the other A sizes at 300 DPI:

• A5 (148 × 210 mm): 1748 × 2480 px
• A3 (297 × 420 mm): 3508 × 4961 px

The A4 height, 3508, becomes the A3 width, and the A4 width, 2480, becomes the A5 height: the halving rule carries straight through to pixels.

Which DPI to use

72 DPI comes from the PostScript point: there are exactly 72 points in an inch, so an A4 PDF page is 595 × 842 points. A pixel count at 72 DPI is really a point count, which is why layout programs and PDF viewers report that value. It is too coarse for printing text or photos.

96 DPI is the CSS reference pixel, the ratio browsers assume between pixels and inches. An A4 page laid out for the web at 100 percent zoom is 794 × 1123 CSS pixels. A screen's real pixel density is usually different, so 794 CSS pixels only measures 210 mm on a calibrated display; see how we calculate accuracy for the details.

150 DPI is a common scanner default and a reasonable minimum for documents that will be read on paper but do not need fine detail. Its files hold one quarter as many pixels as the 300 DPI equivalent.

300 DPI is the usual target for printing text and photographs, and most print services ask for artwork at this resolution. 600 DPI and above suit line art and small type, where edges must stay crisp under magnification. When in doubt for print, prepare the file at 300 DPI; downsampling later is harmless, but upsampling cannot invent detail.

A4 versus US Letter

North America uses US Letter, 8.5 × 11 in, which is 215.9 × 279.4 mm. Letter is 5.9 mm wider and 17.6 mm shorter than A4, and its aspect ratio is 1 : 1.294 rather than 1 : 1.414.

Because Letter is defined in inches, its pixel counts are whole numbers at every listed resolution. Printed on Letter paper without adjustment, an A4 document loses its bottom 17.6 mm; with "fit to page" on, the whole page shrinks and nothing on it is at true size anymore.

Checking a printout at 100 percent

When a document must print at true scale, such as a sewing pattern or a paper template, verify it instead of trusting the print dialog.

1. In the print dialog choose "Actual size" or "100 percent," not "Fit to page" or "Shrink to fit."
2. Measure the printed page. A4 should be 210 mm across its short edge and 297 mm along its long edge.
3. Hold the sheet against a calibrated centimeter ruler on your screen, or against any element on the page with a stated length, such as a 10 cm scale bar. The printed bar and the on-screen ruler should agree.
4. If everything is small by a consistent factor, the printer applied scaling. A 10 cm bar that measures 9.4 cm indicates a 94 percent scale, the ratio produced when A4 content is squeezed onto Letter.

For a scanned page, the process runs in reverse. Scan at 300 DPI and an A4 sheet should come out 2480 × 3508 px; then 1 mm is 300 / 25.4 ≈ 11.81 px. You can confirm that scale by loading the scan into the image measurement tool and marking the page's short edge as 210 mm; every other distance on the page can then be read in millimeters. For other paper sizes, the unit converter moves between millimeters, inches, and points.