Convert Centimeters to Millimeters – Length Converter
This converter converts lengths expressed in centimeters (cm) to millimeters (mm). It follows SI unit relationships so results are exact for arithmetic conversion and suitable for engineering, lab, and everyday use.
Use this tool when you need a reliable, standards-consistent conversion. For measurement work that affects compliance, manufacturing tolerances, or laboratory records, consult instrument specifications and calibration certificates to account for uncertainty.
Interactive Converter
Convert between centimeter and millimeter with precision rounding.
Quick reference table
| Centimeter | Millimeter |
|---|---|
| 1 cm | 10 mm |
| 5 cm | 50 mm |
| 10 cm | 100 mm |
| 25 cm | 250 mm |
| 50 cm | 500 mm |
| 100 cm | 1,000 mm |
Methodology
Centimeters and millimetres are SI-compatible metric units of length. The conversion is a fixed ratio derived from the definitions of the metre in the International System of Units (SI). Authoritative references include the BIPM SI brochure and NIST guidance on SI units.
For practical measurement work, apply the arithmetic conversion first and then consider instrument resolution and calibration traceability. When reporting results, state the converted value with appropriate significant figures and, where required, the instrument uncertainty or calibration status.
Worked examples
1 cm → 10 mm
2.54 cm → 25.4 mm (common conversion: 1 inch = 2.54 cm → 25.4 mm)
0.123 cm → 1.23 mm
100 cm → 1000 mm
Further resources
Expert Q&A
How many millimetres are in one centimetre?
One centimetre equals ten millimetres. The exact arithmetic relationship is 1 cm = 10 mm.
Do I need to worry about rounding when converting?
The mathematical conversion is exact. Rounding matters when you report results: match rounding to the measuring instrument's resolution and to required significant figures. For example, if a ruler reads to the nearest millimetre, report to ±1 mm accordingly.
Can I convert fractional centimetres?
Yes. Multiply any decimal centimetre value by 10 to obtain millimetres (for example, 2.345 cm × 10 = 23.45 mm). Then round or report uncertainty based on instrument precision.
How should I account for instrument limits and uncertainty?
Check the instrument's smallest division and its calibration certificate. State the measurement result with uncertainty or repeatability limits as required by your procedure. For calibration and uncertainty best practices, follow guidance from national metrology institutes such as NIST.
When is traceability to a standards body necessary?
Traceability is recommended whenever measurements are used for regulatory compliance, quality control, procurement tolerances, or laboratory records. Traceability to national standards (for example, calibration traceable to NIST) ensures comparability and defensibility of measurements.
Does this converter comply with SI unit rules?
Yes. The conversion uses the SI-compatible relationship between centimetres and millimetres. For authoritative SI rules, consult the BIPM SI brochure and NIST guidance on the use of SI units.
Sources & citations
- BIPM — The International System of Units (SI) brochure — https://www.bipm.org/en/publications/si-brochure
- NIST — Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — https://physics.nist.gov/cuu/pdf/sp811.pdf
- NIST — Metric (SI) Units and US Practice — https://www.nist.gov/pml/weights-and-measures/metric-si
- NIST — Calibration Services and Traceability — https://www.nist.gov/calibrations
- MIT OpenCourseWare — Fundamentals and use of units (educational resource) — https://ocw.mit.edu