Pixels to centimetres

Pixels to centimetres and millimetres, and back, with A-series paper in whole pixels.

96 px to the inch, fixed by the CSS spec.

pixelscentimetres

100px ÷ 37.7953 = 2.6458cm (96 px per inch ÷ 2.54)

The same value in every unit

points
75pt
100px ÷ 1.3333 = 75pt (96 px per inch ÷ 72)
inches
1.0417in
100px ÷ 96 = 1.0417in (96 px per inch)
millimetres
26.4583mm
100px ÷ 3.7795 = 26.4583mm (96 px per inch ÷ 25.4)
picas
6.25pc
100px ÷ 16 = 6.25pc (96 px per inch ÷ 6)

In short

In CSS, 1 centimetre is 37.7953 pixels and 1 millimetre is 3.7795 pixels, because an inch is 96 pixels and 2.54 centimetres. For print, divide the resolution by 2.54: at 300 ppi a centimetre is 118.11 pixels, so an A4 page needs 2480 × 3508 pixels.

The formula

CSS:   cm = px × 2.54 ÷ 96
       px = cm × 96 ÷ 2.54
Print: cm = px × 2.54 ÷ ppi
       px = cm × ppi ÷ 2.54
       mm = cm × 10

Reference tables

Computed by the same code as the converter above.

Pixels to centimetres and millimetres
pixels	CSS, cm	CSS, mm	Print 300 ppi, cm	Print 300 ppi, mm
1px	0.0265cm	0.2646mm	0.0085cm	0.0847mm
10px	0.2646cm	2.6458mm	0.0847cm	0.8467mm
50px	1.3229cm	13.2292mm	0.4233cm	4.2333mm
96px	2.54cm	25.4mm	0.8128cm	8.128mm
100px	2.6458cm	26.4583mm	0.8467cm	8.4667mm
300px	7.9375cm	79.375mm	2.54cm	25.4mm
500px	13.2292cm	132.2917mm	4.2333cm	42.3333mm
1000px	26.4583cm	264.5833mm	8.4667cm	84.6667mm
1920px	50.8cm	508mm	16.256cm	162.56mm
2480px	65.6167cm	656.1667mm	20.9973cm	209.9733mm
3508px	92.8158cm	928.1583mm	29.7011cm	297.0107mm

Millimetres to pixels
millimetres	CSS	Printed at 150 ppi	Printed at 300 ppi
1mm	3.78px	5.91px	11.81px
3mm	11.34px	17.72px	35.43px
5mm	18.9px	29.53px	59.06px
10mm	37.8px	59.06px	118.11px
25.4mm	96px	150px	300px
50mm	188.98px	295.28px	590.55px
100mm	377.95px	590.55px	1181.1px
148mm	559.37px	874.02px	1748.03px
210mm	793.7px	1240.16px	2480.31px
297mm	1122.52px	1753.94px	3507.87px
420mm	1587.4px	2480.31px	4960.63px

Metric print: paper sizes, bleed and the half-pixel

A-series paper is defined in millimetres (ISO 216): A4 is 210 × 297 mm. At 300 ppi that is 2480.31 × 3507.87 pixels, which is why the figure everyone quotes is 2480 × 3508. A pixel cannot be split, so the honest answer is always rounded, and the rounding moves the printed edge by less than half a pixel, under 0.05 mm at 300 ppi.

Printers usually ask for 3 mm of bleed on every side. At 300 ppi that is 35.43 pixels, so 35 or 36 depending on which way you round; add it to both edges, which makes an A4 file with bleed 2551 × 3579 pixels.

CSS millimetres are not real millimetres on screen. A CSS mm is 96 ÷ 25.4 = 3.7795 CSS pixels, and on a phone that will measure noticeably shorter than a millimetre on a ruler. In a print stylesheet, though, CSS mm are physical, which is the one place writing CSS in millimetres makes sense.

Worked examples

Real sizes, with the sums.

An A5 flyer from a 300 ppi file

You give it

148 × 210 mm at 300 ppi.

You get

148 ÷ 25.4 × 300 = 1748.03 and 210 ÷ 25.4 × 300 = 2480.31, so 1748 × 2480 pixels: half an A4 page turned on its side, give or take the half millimetre ISO 216 rounds away.

A business card with bleed

You give it

An 85 × 55 mm card, 3 mm bleed each side, at 300 ppi.

You get

91 × 61 mm including bleed, which is 1074.80 × 720.47 pixels: make the file 1075 × 720 pixels and keep text 3 mm inside the trim.

Questions people ask

Straight answers. Each one links directly: copy the address after opening it.

How many pixels is 1 cm?

In CSS, 37.7953 pixels. For print it depends on the resolution: 59.06 pixels at 150 ppi and 118.11 at 300 ppi.

How many pixels is A4?

At 300 ppi, 2480 × 3508. At 150 ppi, 1240 × 1754. As a CSS page, 794 × 1123 pixels, which is the width a browser lays out an A4 print stylesheet at.

How do I convert mm to px?

Multiply millimetres by 3.7795 for CSS pixels, or by the print resolution divided by 25.4 for an image: at 300 ppi that is 11.811 pixels per millimetre. Choose millimetres in the converter and it does both.