How many millimetres are in a CSS pixel?

1 CSS pixel = 0.264583333 millimetres. In the other direction, 1 millimetre = 3.779527559 CSS pixels.

A CSS pixel is a reference unit of 1/96 inch, not a physical device pixel. Browsers scale it by the device pixel ratio, so one CSS pixel may cover four hardware pixels on a 2× display.

What is a millimetre?

One millimetre is 3.7795275590551 CSS pixels at the CSS reference resolution of 96 DPI. Real print output should be computed against the actual device DPI instead.

How many millimetres is 100 px?

At 96 px per inch, 100 px is 26.46 mm.

Unit-To-Unit Pixels conversion

PX to MM

1 CSS pixel = 0.264583333 millimetres

At the CSS reference resolution of 96 DPI, one pixel is 0.264583 mm. This is a fixed ratio inside CSS and not a statement about your monitor.

Formula mm = px × 0.264583333333

CSS pixel (px) max 24 digits

Millimetre (mm) max 24 digits

Type in either field — the other updates on every keystroke. Need other units? Open the full pixels converter.

PX to MM — quick reference
CSS pixel	Millimetre
1 px	0.264583 mm
2 px	0.529167 mm
3 px	0.79375 mm
4 px	1.058333 mm
5 px	1.322917 mm
10 px	2.645833 mm
15 px	3.96875 mm
20 px	5.291667 mm
25 px	6.614583 mm
50 px	13.229167 mm
100 px	26.458333 mm
500 px	132.291667 mm
1000 px	264.583333 mm

MM to PX — reverse
Millimetre	CSS pixel
1 mm	3.779528 px
2 mm	7.559055 px
3 mm	11.338583 px
4 mm	15.11811 px
5 mm	18.897638 px
10 mm	37.795276 px
15 mm	56.692913 px
20 mm	75.590551 px
25 mm	94.488189 px
50 mm	188.976378 px
100 mm	377.952756 px
500 mm	1889.76378 px
1000 mm	3779.527559 px

Worked examples

Common values
Situation	From	To
Hairline border	1 px	0.2646 mm
Icon	24 px	6.35 mm
Button height	48 px	12.7 mm
Phone width	390 px	103.2 mm
Tablet width	768 px	203.2 mm
A4 paper width	794 px	210.1 mm

Mental-math shortcut

Multiply by 0.265, or divide by 3.78. 100 px is about 26.5 mm.

Where this conversion comes up

Design hand-offs for print, signage or laser cutting need millimetres. A4 paper (210 × 297 mm) is about 794 × 1123 px at 96 PPI.

Common mistakes

The 0.2646 factor only holds at 96 PPI. At 300 PPI one pixel is 0.0847 mm, so the same file prints much smaller.

Background

An inch is exactly 25.4 mm and a CSS pixel is 1/96 inch, so one pixel is 25.4 ÷ 96 mm.

Learn more

One CSS pixel is 1/96 of an inch, which is about 0.2646 mm. In print at 300 PPI, one image pixel covers only about 0.0847 mm.

Frequently asked

How many millimetres are in a CSS pixel?: 1 CSS pixel = 0.264583333 millimetres. In the other direction, 1 millimetre = 3.779527559 CSS pixels.
What is a CSS pixel?: A CSS pixel is a reference unit of 1/96 inch, not a physical device pixel. Browsers scale it by the device pixel ratio, so one CSS pixel may cover four hardware pixels on a 2× display.
What is a millimetre?: One millimetre is 3.7795275590551 CSS pixels at the CSS reference resolution of 96 DPI. Real print output should be computed against the actual device DPI instead.
How many millimetres is 100 px?: At 96 px per inch, 100 px is 26.46 mm.

Related pixels conversions

PX to REM REM to PX PX to PT PT to PX PX to Inches DP to PX