Millimeters to Centimeters (mm to cm): Formula, Chart and Examples

Quick answer: 1 mm = 0.1 cm. To convert, multiply the mm value by 0.1; to go back, divide.

Millimeters to centimeters is a ÷10: 45 mm = 4.5 cm, 8 mm = 0.8 cm — move the decimal point one place left. Product specs, rainfall, drill bits and engineering drawings quote mm; rulers, sewing patterns and body measurements quote cm.

The formula

cm = mm × 0.1 · mm = cm ÷ 0.1

Common values

mm	cm	also
1 mm	0.1 cm	0.039 in
2.5 mm	0.25 cm	0.098 in
4.5 mm	0.45 cm	0.177 in
5 mm	0.5 cm	0.197 in
10 mm	1 cm	0.394 in
12.5 mm	1.25 cm	0.492 in
15 mm	1.5 cm	0.591 in
20 mm	2 cm	0.787 in
25 mm	2.5 cm	0.984 in
30 mm	3 cm	1.181 in
45 mm	4.5 cm	1.772 in
50 mm	5 cm	1.969 in
75 mm	7.5 cm	2.953 in
100 mm	10 cm	3.937 in
250 mm	25 cm	9.843 in

4.5 mm to cm: 0.45 cm

4.5 mm = 0.45 cm — 0.177 in. Working: 4.5 × 0.1 = 0.45.

4.5 mm is 0.45 cm — a shade under 3/16 of an inch (0.177 in). It is a common drill-bit and screw size (M4.5), the thickness of standard window glass and many phone bezels, and a 4.5 mm knitting needle is a UK size 7 / US size 7.

The other way: cm to mm

cm	mm
1 cm	10 mm
2 cm	20 mm
5 cm	50 mm
10 cm	100 mm
12 cm	120 mm
15 cm	150 mm
20 cm	200 mm
25 cm	250 mm
50 cm	500 mm
100 cm	1,000 mm

Common mistake

Moving the decimal two places (that is mm→dm or cm→m). Between mm and cm it is exactly one place.

Frequently asked questions

Is the conversion exact?

Yes — the factor follows from the legal definition of the units (1 in = 25.4 mm and 1 ft = 0.3048 m), so the only rounding is in the last decimal place shown.

How do I convert a different value?

Use the mm to cm converter for any number, or the length conversion guide for every length unit and formula in one place.