Free Cm to Mm Converter
Published: 14 November 2026 · Updated: 14 November 2026
Type a length in centimetres and the exact value in millimetres appears instantly — it is the simplest conversion in the metric system, a shift of the decimal point by one place. The converter works both ways, so millimetres convert back to centimetres too. It starts with 25 cm, which is 250 mm. For the reverse tool, use the Free Mm to Cm Converter.
1 cm is exactly 10 mm, so multiply any centimetre value by 10. That makes 25 cm equal to 250 mm. Moving from centimetres to millimetres only moves the decimal point one place to the right — 7.5 cm becomes 75 mm — with no rounding and no fractions.
Researched by MixKhazana Team · Last updated 14 November 2026 · Data: NIST SP 811; BIPM SI Brochure; International Yard and Pound Agreement 1959
What is a centimetre?
A centimetre (cm) is one hundredth of a metre: 1 cm = 0.01 m. It is the metric unit used for everyday lengths across Europe — heights, waist sizes, furniture, paper sizes and rainfall.
One centimetre is about the width of an adult fingernail. Because the metric system is decimal, every step between units is a power of ten: 10 mm make 1 cm, and 100 cm make 1 m.
What is a millimetre?
A millimetre (mm) is one thousandth of a metre: 1 mm = 0.001 m, and 10 mm = 1 cm. It is the smallest metric unit in everyday use, and the standard unit for precision work.
Millimetres are used for engineering drawings, drill bits, screw lengths, paper thickness, jewellery and rain gauges — anywhere a centimetre would be too coarse and decimals would be fiddly. The American spelling is millimeter.
How to use this converter
- Type your length in the centimetres box — millimetres appear as you type.
- Decimals work exactly as expected: 2.4 cm becomes 24 mm, and 0.5 cm becomes 5 mm.
- To convert back, type in the millimetres box or press Swap direction, which flips the converter and carries the converted value over.
- The result line also shows the reverse rate: 1 mm = 0.1 cm.
Centimetres to millimetres formula
Let Lcm be the length in centimetres and Lmm be the same length in millimetres:
- Millimetres from centimetres: Lmm = Lcm × 10
- Centimetres from millimetres: Lcm = Lmm ÷ 10
Both directions are exact: the millimetre is defined as one tenth of a centimetre, so no rounding is ever involved. For the wider picture, see our metric vs imperial conversion guide for Europe.
Worked example
A picture-frame rebate (the groove the glass sits in) is 2.4 cm deep, and the glass supplier quotes in millimetres:
- Multiply by 10: 2.4 × 10 = 24 mm
- Split it up: 2 × 10 = 20, and 0.4 × 10 = 4, giving 20 + 4 = 24 mm
- Check: 24 ÷ 10 = 2.4 cm, back where we started
So order glass cut for a 24 mm rebate. Try 2.4 in the converter above.
Centimetres to millimetres conversion table
| Centimetres (cm) | Millimetres (mm) |
| 0.5 | 5 |
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 40 |
| 6 | 60 |
| 7.5 | 75 |
| 9 | 90 |
| 12 | 120 |
| 15 | 150 |
| 18 | 180 |
| 21 | 210 |
| 25 | 250 |
| 30 | 300 |
| 45 | 450 |
| 60 | 600 |
Millimetres are whole numbers here because multiplying by 10 only moves the decimal point.
Everyday benchmarks: centimetre sizes in millimetres
These everyday centimetre lengths are often quoted in millimetres instead:
- Credit card thickness — 0.076 cm = 0.76 mm. The ISO standard card is 0.76 mm thick.
- A4 paper width — 21 cm = 210 mm. A4 is 210 × 297 mm, the size printers and copiers expect.
- Standard pencil — 0.7 cm = 7 mm across. A hexagonal pencil is about 7 mm from flat to flat.
- One-euro coin — 2.325 cm = 23.25 mm across. The €1 coin is 23.25 mm in diameter.
- Phone width — 7.8 cm = 78 mm. A typical smartphone is 75–80 mm wide.
- Photo print — 10 cm = 100 mm. A 10 × 15 cm print is 100 × 150 mm, the 4 × 6 inch standard.
For units beyond the metric length scale, the Free Unit Converter covers more units in one place, including inches, feet, weight and temperature.
Frequently asked questions
How do you convert cm to mm?
Multiply the centimetre value by 10. For example, 8 cm × 10 = 80 mm. The conversion is exact: a millimetre is defined as one tenth of a centimetre, so it only moves the decimal point one place.
What is 25 cm in mm?
25 cm is 250 mm. Multiply by 10: 25 × 10 = 250. Twenty-five centimetres is also just under 10 inches.
How many mm is 1 cm?
1 cm is exactly 10 mm. This is true by definition in the metric system, where each step between neighbouring units is a factor of ten.
Is a millimetre bigger than a centimetre?
No, a millimetre is ten times smaller than a centimetre. It takes 10 mm to make 1 cm, just as it takes 100 cm to make 1 m. The smaller the unit, the bigger the number for the same length.
How do I convert 7.5 cm to mm?
Multiply by 10, which moves the decimal point one place right: 7.5 cm = 75 mm. The same trick works for any decimal: 0.3 cm = 3 mm, and 12.25 cm = 122.5 mm.
Why do engineers measure in mm instead of cm?
Millimetres keep numbers whole and avoid decimals: a 243 mm part is clearer on a drawing than 24.3 cm, and mistakes are easier to spot. Workshops, 3D printers and CNC machines all work in millimetres for the same reason.
What is 0.5 cm in mm?
0.5 cm is 5 mm. Half a centimetre is five millimetres, roughly the thickness of two one-euro coins stacked together.
Can I convert mm back to cm here?
Yes. Type in the millimetres box and the centimetre value updates instantly, or press Swap direction. The dedicated reverse tool is the Free Mm to Cm Converter.
Sources
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), conversion factors for the inch, foot and yard.
- BIPM SI Brochure — the International System of Units, definitions of the metre, centimetre and millimetre.
- International Yard and Pound Agreement, 1959 — 1 yard = 0.9144 m exactly, giving 1 in = 25.4 mm and 1 ft = 0.3048 m exactly.
Disclaimer: conversions use the exact defined factor (1 cm = 10 mm); for precision parts, confirm against the drawing or datasheet.
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