Result
All calculations run locally in your browser: parsing, chart, export. Disconnect the network and the page keeps working.
Facts and limits of this method
| mm → pixels formula | pixels = mm / 25.4 × DPI |
|---|---|
| Pixels → mm formula | mm = pixels / DPI × 25.4 |
| 96 DPI | the standard resolution for Windows and the CSS pixel |
| 300 DPI | the typical resolution for high-quality print |
When it misleads you
- A pixel by itself has no fixed physical size — the relationship between pixels and millimeters always depends on the specific resolution (DPI/PPI) of the device or image, which needs to be known in advance or set manually.
- The web's CSS "pixel" is historically defined as 1/96 of an inch (the 96 DPI standard) regardless of a screen's actual physical pixel density, which on modern Retina/HiDPI displays can be 2–3 times higher.
- Print typically uses a higher resolution (150–300 DPI and above) — using web resolution (72–96 DPI) for print will produce a blurry, pixelated image on paper.
- The result is rounded to a fixed 2 decimal places — sufficient for practical layout and prepress work.
How it is calculated
The DPI resolution is converted into pixels per millimeter by dividing by 25.4 (the number of millimeters in an inch).
To convert millimeters to pixels, the entered value in mm is multiplied by this pixels-per-millimeter figure.
To convert pixels to millimeters, the entered value in pixels is divided by the same pixels-per-millimeter figure.
The result and the DPI value used update instantly whenever any parameter changes.
Questions and answers
What DPI should I use for web design?
Generally 96 DPI — the standard for CSS pixels in most browsers; Retina display UI elements have a higher physical pixel density, but the logical CSS pixel remains tied to 96 DPI.
What DPI is needed for high-quality printing?
300 DPI is generally considered the standard for professional printing; for draft or less demanding printing, 150 DPI is often sufficient.
Why millimeters and not centimeters?
Millimeters are a more convenient unit for the small quantities typical in typographic sizes (such as line thickness or layout margins) — avoiding the fractional numbers that centimeters would produce.
Is my data sent anywhere?
No, the whole calculation runs in your browser.