To convert centimeters to millimeters, multiply by 10. So 1 cm = 10 mm, 5 cm = 50 mm, and 30 cm = 300 mm. The factor is exact - 1 cm = 10 mm by the SI metric prefix definition.
- Exact factor: 1 cm = 10 mm (SI prefix definition, no approximation).
- 1 cm = 10 mm. 10 cm = 100 mm. 100 cm = 1000 mm = 1 m.
- The conversion is a simple decimal shift - move the decimal point one place right.
- Common use cases: sewing, woodworking, photography, precision manufacturing.
How to Use This Converter
Type any centimeter value in the cm field and the millimeters result appears instantly. You can also type in the mm field to convert back to centimeters - it works in both directions without pressing a button.
How Do You Convert Centimeters to Millimeters?
Multiply centimeters by 10. The relationship is exact: the SI prefix "centi-" means 1/100 and "milli-" means 1/1000. Since 1/100 ÷ 1/1000 = 10, there are exactly 10 mm in every centimeter.
$$\text{mm} = \text{cm} \times 10$$
Worked examples: 1 cm = 10 mm. 2.5 cm = 25 mm. 30 cm = 300 mm. 100 cm = 1000 mm = 1 m.
Mental shortcut: simply move the decimal point one place to the right. 12.5 cm → 125 mm. This is the simplest conversion in the metric system.
How Do You Convert Millimeters to Centimeters?
Divide millimeters by 10. For a dedicated reverse converter, see the millimeters to centimeters converter.
$$\text{cm} = \text{mm} \div 10$$
Worked examples: 10 mm = 1 cm. 25 mm = 2.5 cm. 300 mm = 30 cm.
Centimeters to Millimeters Reference Table
Common values converted at the exact factor of 10:
| Centimeters | Millimeters | Common context |
|---|---|---|
| 0.5 cm | 5 mm | Standard pencil diameter |
| 1 cm | 10 mm | Small button diameter |
| 2.54 cm | 25.4 mm | Exactly 1 inch |
| 5 cm | 50 mm | Camera filter rim (approx.) |
| 10 cm | 100 mm | Smartphone width (approx.) |
| 15 cm | 150 mm | 6-inch ruler |
| 21 cm | 210 mm | A4 paper width |
| 29.7 cm | 297 mm | A4 paper height |
| 30 cm | 300 mm | Standard 30 cm ruler |
| 50 cm | 500 mm | Half a meter |
| 100 cm | 1000 mm | 1 meter exactly |
When Do You Need to Convert Centimeters to Millimeters?
Both units are used in everyday metric measurement, and conversions happen when precision requirements change:
- Sewing and tailoring - seam allowances and buttonhole sizes are in mm; fabric widths and garment measurements in cm.
- Woodworking and joinery - overall dimensions in cm; tenons, grooves, and fine tolerances in mm.
- Photography and optics - print sizes in cm; lens filter threads, sensor dimensions in mm.
- Medical imaging - anatomy dimensions in cm; lesion sizes, catheter diameters in mm.
- Engineering - product dimensions in cm for readability; tight tolerances specified in mm.
Frequently Asked Questions
How many mm is 1 cm?
Exactly 10 mm. The "centi-" prefix means 1/100 of a meter; "milli-" means 1/1000. So 1 cm = 10 × 1 mm. This holds true for any cm value - just multiply by 10.
How do you convert cm to mm?
Multiply by 10, or move the decimal point one position to the right. 3.7 cm → 37 mm. 0.8 cm → 8 mm. 100 cm → 1000 mm. The conversion is exact with no rounding for any input.
How many mm is 2.5 cm?
2.5 cm equals exactly 25 mm. This is very close to 1 inch (which is 25.4 mm = 2.54 cm). To convert to inches directly, use the centimeters to inches converter.
How many mm is 30 cm?
30 cm equals exactly 300 mm - the length of a standard 30 cm ruler. To convert 30 cm to inches: 30 ÷ 2.54 = 11.811 in. For that conversion use the cm to inches converter.