Convert Pixels to Millimetres for Print (px to mm, 72, 96 and 300 DPI)
"How many millimetres is 1000 pixels?" has no single answer: it depends on the resolution. Pixels only become physical once you pick a DPI (dots or pixels per inch).
The formula
mm = pixels / DPI x 25.4 and the other way pixels = mm / 25.4 x DPI.
Quick chart for 100 pixels
| Resolution | 100 px is | 1 mm is |
|---|---|---|
| 72 DPI | 35.28 mm | 2.83 px |
| 96 DPI (CSS / Windows) | 26.46 mm | 3.78 px |
| 150 DPI | 16.93 mm | 5.91 px |
| 300 DPI (print) | 8.47 mm | 11.81 px |
Examples
- An A4 page at 300 DPI is 2480 x 3508 px.
- A 1200 px wide photo prints 101.6 mm wide at 300 DPI and 304.8 mm at 100 DPI.
- A business card (85 x 55 mm) needs at least 1004 x 650 px at 300 DPI.
Measure the printed size of a PDF directly
If the pixels are already inside a PDF, skip the math: open it in PdfRuler, set the unit to mm and read the real size of a placed image, or use Auto-measure, which reports every placed image in the page's unit. The unit px in PdfRuler means CSS pixels (96 per inch), the convention web designers use.
For the whole picture of how these units fit together, read PDF units explained.
Frequently asked questions
How do I convert pixels to mm?
Divide the pixels by the DPI and multiply by 25.4. At 96 DPI, 100 px is 26.46 mm; at 300 DPI, 100 px is 8.47 mm.
What DPI should I use for print?
Use 300 DPI for sharp print results. 150 DPI is acceptable for large posters viewed from a distance.
How many pixels is A4 at 300 DPI?
A4 is 2480 x 3508 pixels at 300 DPI, and 794 x 1123 pixels at 96 DPI.
