Cm to mm converter

Cm to mm is a single step: multiply by 10, because one centimeter has exactly ten millimeters. Type a value and the millimeters appear as you type, with inches below; mm to cm works in the same box.

Example: Length 2.5 · Direction: Cm to mm → Answer: 2.5 cm = 25 mm. Source: BIPM – SI Brochure (9th edition), Table 7: SI prefixes centi = 10⁻² and milli = 10⁻³ (read 15.10.2026). Updated: 15 October 2026.

Length

Direction

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Result

Answer: 2.5 cm = 25 mm
In inches: In inches: 0.9843 in.
Working: 2.5 cm × 10 = 25 mm
Conversion chart: cm mm
0.1 1
0.5 5
1 10
1.5 15
2 20
2.5 25
3 30
4 40
5 50
7.5 75
10 100
15 150
20 200
25 250
30 300
50 500
100 1,000
Lengths worth knowing: Example cm mm
Mechanical pencil lead (0.5 mm) 0.05 0.5
One inch 2.54 25.4
Width of a credit card (85.6 mm) 8.56 85.6
Width of an A4 sheet 21 210
Height of an A4 sheet 29.7 297; Calculated with 1 cm = 10 mm exactly (SI prefixes centi = 1/100, milli = 1/1000 of a meter). Inches use 1 in = 2.54 cm exactly.

cm	mm
0.1	1
0.5	5
1	10
1.5	15
2	20
2.5	25
3	30
4	40
5	50
7.5	75
10	100
15	150
20	200
25	250
30	300
50	500
100	1,000

Example	cm	mm
Mechanical pencil lead (0.5 mm)	0.05	0.5
One inch	2.54	25.4
Width of a credit card (85.6 mm)	8.56	85.6
Width of an A4 sheet	21	210
Height of an A4 sheet	29.7	297

How it is calculated

How to convert cm to mm

millimeters = centimeters × 10 and centimeters = millimeters ÷ 10. The prefix centi means one hundredth of a meter and milli one thousandth, so one centimeter holds exactly ten millimeters. In practice you move the decimal point one place: 2.5 cm = 25 mm, 0.8 cm = 8 mm, 127 mm = 12.7 cm.

Cm to mm chart

Centimeters	Millimeters
0.5	5
1	10
2.5	25
8.56	85.6
30	300

Reading a ruler

On a metric ruler the long numbered marks are centimeters and the small marks between them are millimeters. A screw that ends three small marks after the 4 is 4.3 cm, or 43 mm. Ring sizes, jewelry, screws and drawings are usually given in millimeters, while body measurements and furniture use centimeters.

Common mistakes

Two slips come up again and again. The first is moving the decimal point the wrong way, which turns twenty-five millimeters into a quarter of a millimeter. The second is mixing up the small marks on a ruler with half-centimeter marks: many rulers draw the fifth millimeter longer, but it is still one millimeter like the others. If a result looks strange, picture it on the ruler before you cut, drill or order.

Centimeters and inches

One inch is exactly 2.54 cm, which is 25.4 mm, so 1 cm is about 0.3937 in. The converter shows the inch value under each result. For a full inch conversion use inches to cm or mm to inches; meters, feet and miles are in the length converter.

Frequently asked questions

How many mm are in 1 cm?

Exactly ten. Multiply centimeters by 10 to get millimeters.

How do I convert mm to cm?

Divide by 10, or move the decimal point one place to the left: 85.6 mm = 8.56 cm.

What is 2.5 cm in mm?

Two and a half centimeters are 25 millimeters.

How many mm is 30 cm?

30 cm = 300 mm, the length of a common school ruler.

Is 1 mm smaller than 1 cm?

Yes. A millimeter is one tenth of a centimeter, so 1 mm = 0.1 cm.

Sources and legal basis

As of: 15 October 2026 · Editorial policy