MM to CM converter, millimeters to centimeters.

To convert mm to cm, divide the millimeters by 10. So 25 mm is 2.5 cm, 8 mm is 0.8 cm and 150 mm is 15 cm. The cards also show meters, inches and feet. 25 mm is 0.9843 inches.

How to use the converter

1. Type a length in the Millimeters (mm) box. The Centimeters (cm) box and the big result follow as you type.
2. Look at the cards under the result for the same length in other units. Choose Decimals in the side column to fix the number of places.
3. Click a row in Common values to load it. Use Copy result, Copy link, Copy table or Print chart to keep the answer, the ⇄ button to go the other way and Start again to reset.

Where the factor comes from

The NIST list of metric (SI) prefixes gives kilo as a thousand, centi as a hundredth and milli as a thousandth (checked 24 Oct 2026). A millimeter is a thousandth of a meter and a centimeter is a hundredth, so ten millimeters make a centimeter.

On a ruler

The long numbered marks on a metric ruler are centimeters, and the small marks between them are millimeters. There are ten small steps between two numbers. A point 3 marks past the 4 reads 4.3 cm, which is 43 mm. To go from the ruler to a drawing in millimeters, multiply the whole number by 10 and add the small marks. In reverse, divide by 10 and the last digit is the small marks.

Millimeters in centimeters

Worked examples

• A screw 18 mm long. 1.8 cm.
• A sheet 297 mm tall. 29.7 cm.
• A gap of 3.5 mm. 0.35 cm, which is 0.1378 inches.
• A strip of 1,200 mm. 120 cm, or 1.2 m.

A quick check in your head

Take off the last digit and put it after a point. 47 mm becomes 4.7 cm. 120 mm becomes 12.0 cm. If a measurement ends in 0, the centimeter figure is a whole number: 250 mm is 25 cm. A check is that 10 mm must give exactly 1 cm.

Where you meet it

Specifications for screws, tiles, glass and paper use millimeters, while a person measuring with a ruler thinks in centimeters. A tile of 600 mm is 60 cm, and a glass sheet 4 mm thick is 0.4 cm. Convert once and keep the unit in the note.

Write the sum as a unit chain

A unit chain shows why the sum works. Write the length, then a fraction that equals 1 with the unit you want on top: 25 mm × 0.1 cm / 1 mm = 2.5 cm. The mm on the left cancels the mm under the line, and only cm is left. You can also go through a third unit, meters, in two steps: 25 mm × 0.001 m / 1 mm × 100 cm / 1 m = 0.025 m × 100 cm / 1 m = 2.5 cm. Both routes give the same answer, which is a handy check when a factor looks odd. If the wrong unit is left over, the fraction is upside down.

Squares and cubes of the same factor

The factor changes when you convert an area or a volume. Square it for an area and cube it for a volume. The reason is that an area has two lengths in it and a volume has three. Take a square with a side of 25 mm. Its side is 2.5 cm. Its area is 25 × 25 = 625 mm², and in the other unit it is 2.5 × 2.5 = 6.25 cm². The area factor is the length factor squared, which is 0.01.

Mixed units in one measurement

Lengths are often given in two or three units, such as 4 cm 7 mm. Convert each part to centimeters, then add. 4 cm stays 4 cm; 7 mm = 0.7 cm. The total is 4.7 cm. Rounded parts can drift in the last digit, so when the parts are not exact, convert the whole once instead. In millimeters the same length is 47 mm.

The metric ladder

Read along a row: the row is one of that unit, and each column says how many of the column unit it holds. Exact values are shown in full. Long ones are rounded to five decimals.

Check by converting back

Type the number 25 in the Millimeters box and note the answer, 2.5 cm. Now press the ⇄ button, so the answer becomes the input. It should return 25 mm. If it does not, one of the boxes was read wrongly. This takes two seconds and catches a slipped decimal point.

Mistakes to avoid

Dividing by 100 is the usual slip, as if the answer were in meters. A 25 mm part is 2.5 cm, not 0.25. Keep area apart from length: 100 mm² is 1 cm², since the factor is 10 × 10. The MM to inches converter handles inches.