Convert millimeters to pixels at any DPI

At the standard 96 DPI screen one millimeter is about 3.78 pixels, and at 300 DPI print resolution it is 11.81 pixels. Both numbers follow from the resolution, because a pixel describes a point of an image and a millimeter a length on paper. The one-to-one match appears at exactly 25.4 DPI, since an inch holds 25.4 millimeters — a resolution nobody prints or designs at.

It depends entirely on the resolution you set. At the standard 96 DPI screen resolution, one millimeter is about 3.78 pixels, and at the 300 DPI used for print, 11.81 pixels. To convert any number of millimeters to pixels, multiply it by the DPI and divide by 25.4.

The formula comes from a fixed relationship: one inch is exactly 25.4 mm. The full formula is pixels = millimeters × DPI ÷ 25.4. It also works in reverse: millimeters = pixels × 25.4 ÷ DPI. You only need two values — the dimension and the target resolution — to instantly calculate the third.

The simplest way is to type the dimension in millimeters into the converter field and pick the DPI you need — the result appears instantly. If you would rather calculate it by hand, use the formula: pixels = millimeters × DPI ÷ 25.4. For 20 mm at 96 DPI, you get 20 × 96 ÷ 25.4, or about 76 pixels.

Twenty millimeters on a 96 DPI screen is about 76 pixels. At 300 DPI print resolution, the same value grows to 236 pixels, and at 600 DPI used for high-quality photo printing it reaches 472 pixels.

One hundred millimeters (10 cm) at 96 DPI is about 378 pixels. At 300 DPI print resolution, the same 100 mm is exactly 1,181 pixels — a value worth remembering, since it is the short edge of a classic 10×15 cm photo print.

A pixel (px) is a digital unit, not a physical length measurement — it has no fixed millimeter equivalent until you set a DPI or PPI resolution. In practice, 1 pixel at 96 DPI (screen standard) is about 0.265 mm, while at 300 DPI (print standard) it is only 0.085 mm.

A Polish business card at 90 × 50 mm is 1,063 × 591 px at 300 DPI. A European business card at 85 × 55 mm is 1,004 × 650 px at the same resolution. After adding the standard 3 mm bleed on every edge, the dimensions grow to 96 × 56 mm, or about 1,134 × 661 px.

Bleed is extra margin, usually 3–5 mm, around your design that gets trimmed off after printing. It prevents white edges if the cutting machine is slightly off. At 300 DPI, the standard 3 mm bleed is an extra 35 pixels per side — that is how much bigger your file should be than the final trimmed format.

An A4 sheet is 210 × 297 mm, which is exactly 2,480 × 3,508 pixels at 300 DPI. At 150 DPI, the same dimensions are 1,240 × 1,754 pixels, and at a screen resolution of 96 DPI just 794 × 1,123 pixels.

300 DPI is the standard for both offset and digital printing — most print shops require this value. For large formats like A1 or A0 posters, 150 DPI is often enough, since they are viewed from a greater distance. Large-format banners and billboards are sometimes printed at just 30–72 DPI.

In Adobe Illustrator, go to Edit › Preferences › Units and choose Millimeters — the unit changes across all panels and rulers immediately. InDesign works similarly and uses millimeters by default. In both programs, the resulting pixel count depends on the resolution set when exporting the file, usually 300 DPI for print. You will find detailed guides for Illustrator, InDesign, CorelDRAW, Photoshop, Figma, and Canva in the section above.

DPI (dots per inch) is the number of ink dots per inch of material and is a printer specification. PPI (pixels per inch) is the number of pixels per inch of screen and describes a monitor or display. In everyday use, designers use both terms interchangeably, but technically DPI applies to print and PPI to screens.

In CSS stylesheets the mm unit is converted with a fixed formula: 1mm = 96px ÷ 25.4 ≈ 3.78px, regardless of the device. The same constant applies in SVG files, where dimensions can be written directly in millimeters. In practice, web interfaces use px, rem or em units, while mm is reserved for print stylesheets (@media print).

The ISO ID-1 standard, which applies to payment cards, ID cards, and driving licences, is exactly 85.60 × 53.98 mm.[2] At 300 DPI, that comes out to 1,011 × 638 pixels. This is a more precise figure than the common 85 × 55 mm rounding sometimes used for European business cards.

Forty pixels on a 96 DPI screen is about 10.58 mm, just over 1 cm. At 300 DPI print resolution, the same number of pixels only takes up 3.39 mm. The higher the DPI, the less physical space a given number of pixels occupies.

Yes, our converter works in both directions. Type the number of pixels into the right field, or use the Reverse button to flip the conversion direction — the result in millimeters appears instantly. The formula for this direction is millimeters = pixels × 25.4 ÷ DPI.