Last updated: September 16, 2026
Quick answer: Multiply centimeters by 10 to get millimeters. 1 cm = 10 mm. So 2.5 cm = 25 mm, 15 cm = 150 mm, and 30 cm (a standard ruler) = 300 mm. It's the simplest metric conversion there is.
Centimeter to Millimeter
Instantly convert centimeter to millimeter with fast, accurate, real-time results.
Centimeters and millimeters are both metric units of length — just one decimal step apart. The conversion is instant: move the decimal point one place to the right. Engineers, machinists, 3D printing enthusiasts, and tailors all work in millimeters for precision, while everyday measurements (height, furniture, fabric) tend to stay in centimeters. This page covers the formula, practical reference tables, and the reverse mm to cm converter.
Formula: cm to mm
Since 1 centimeter is exactly 10 millimeters, the conversion is just multiplication by 10. In the SI system, the prefix "centi-" means 1/100 and "milli-" means 1/1000 — so a centimeter is 10 millimeters. For the reverse, see the mm to cm converter (divide by 10).
Quick mental shortcuts
- Move the decimal one place right: 3.7 cm → 37 mm
- Double-digit cm → triple-digit mm: 12 cm → 120 mm
- Centimeters end in 0 mm: 5 cm = 50 mm, 8 cm = 80 mm
Reading a Ruler: cm vs mm Markings
A standard metric ruler has two sets of lines. The longer numbered lines mark centimeters (1 cm apart). The shorter lines between them mark millimeters — there are 9 small lines between each pair of cm marks (dividing the space into 10 equal 1 mm segments).
| What you read on the ruler | In mm | Meaning |
|---|---|---|
| The "1" mark | 10 mm | 1 centimeter |
| 1 small mark past "2" | 21 mm | 2.1 cm |
| The "5" mark | 50 mm | 5 centimeters |
| Halfway between 7 and 8 | 75 mm | 7.5 cm |
| The "30" mark (end of ruler) | 300 mm | 30 centimeters |
3D Printing and Engineering Reference
In 3D printing, CNC machining, and engineering drawings, millimeters are the standard unit. If your design software (like Fusion 360, SolidWorks, or Cura) asks for dimensions, enter them in mm. Here are common object sizes in both units:
| Object / dimension | cm | mm | Notes |
|---|---|---|---|
| Standard FDM nozzle diameter | 0.04 cm | 0.4 mm | Most common nozzle size |
| Layer height (fine) | 0.01 cm | 0.1 mm | High-detail printing |
| Layer height (standard) | 0.02 cm | 0.2 mm | Common default |
| M3 bolt diameter | 0.3 cm | 3 mm | Common metric screw |
| M6 bolt diameter | 0.6 cm | 6 mm | Furniture assembly bolts |
| Filament diameter (FDM) | 0.175 cm | 1.75 mm | Standard FDM filament |
| PCB thickness (standard) | 0.16 cm | 1.6 mm | Most circuit boards |
| Standard A4 paper width | 21 cm | 210 mm | ISO 216 A4 |
| Credit card width | 8.56 cm | 85.6 mm | ISO/IEC 7810 ID-1 |
| 10 cm print bed margin | 10 cm | 100 mm | Common clearance |
Sewing and Fabric Guide
Sewing patterns often list seam allowances and hem widths in both cm and mm. Here are standard tailoring dimensions:
| Sewing term | cm | mm |
|---|---|---|
| Narrow seam allowance | 0.6 cm | 6 mm |
| Standard seam allowance (EU) | 1.5 cm | 15 mm |
| Standard seam allowance (US) | 1.6 cm | 16 mm (⅝ in) |
| Narrow hem (shirt) | 0.6–1 cm | 6–10 mm |
| Standard hem (trousers) | 3–4 cm | 30–40 mm |
| Wide hem (skirt, dress) | 5 cm | 50 mm |
| Buttonhole length (shirt) | 2–2.5 cm | 20–25 mm |
| Ribbon width (narrow) | 0.6 cm | 6 mm |
| Ribbon width (wide) | 2.5 cm | 25 mm |
Full cm to mm Table
| cm | mm | cm | mm |
|---|---|---|---|
| 0.1 cm | 1 mm | 10 cm | 100 mm |
| 0.2 cm | 2 mm | 12 cm | 120 mm |
| 0.3 cm | 3 mm | 15 cm | 150 mm |
| 0.4 cm | 4 mm | 20 cm | 200 mm |
| 0.5 cm | 5 mm | 25 cm | 250 mm |
| 0.6 cm | 6 mm | 30 cm | 300 mm |
| 0.7 cm | 7 mm | 35 cm | 350 mm |
| 0.8 cm | 8 mm | 40 cm | 400 mm |
| 0.9 cm | 9 mm | 45 cm | 450 mm |
| 1 cm | 10 mm | 50 cm | 500 mm |
| 1.5 cm | 15 mm | 60 cm | 600 mm |
| 2 cm | 20 mm | 70 cm | 700 mm |
| 2.5 cm | 25 mm | 75 cm | 750 mm |
| 3 cm | 30 mm | 80 cm | 800 mm |
| 4 cm | 40 mm | 90 cm | 900 mm |
| 5 cm | 50 mm | 100 cm | 1,000 mm |
| 6 cm | 60 mm | 150 cm | 1,500 mm |
| 7 cm | 70 mm | 200 cm | 2,000 mm |
| 8 cm | 80 mm | 250 cm | 2,500 mm |
| 9 cm | 90 mm | 300 cm | 3,000 mm |
FAQs About cm to mm
How many mm is 1 cm?
1 centimeter = 10 millimeters exactly. This is a fixed definition in the metric (SI) system. The prefix "centi-" means 1/100 of a meter, and "milli-" means 1/1000 — so 1 cm = 10 mm.
How do I convert cm to mm without a calculator?
Simply multiply by 10 — which means moving the decimal point one place to the right. For example: 3.5 cm → 35 mm; 0.8 cm → 8 mm; 12.7 cm → 127 mm. No calculator needed.
Is 25 mm the same as 2.5 cm?
Yes, exactly. 25 mm ÷ 10 = 2.5 cm. This is a common size for wide seam tape, certain pipe fittings, and battery dimensions (AAA battery diameter is about 10.5 mm = 1.05 cm).
Why do engineers use mm instead of cm?
Millimeters are preferred in engineering because they produce whole numbers for most practical dimensions, avoiding decimals. A 50 mm bolt is cleaner to work with than a 5 cm bolt, and the risk of confusing millimeters with centimeters is eliminated when all measurements stay in one unit.
How many mm is 170 cm (average adult height)?
170 cm × 10 = 1,700 mm. This is also equal to 1.7 meters. Heights are rarely expressed in millimeters, but the conversion works the same way.
What is 5 cm in mm?
5 cm = 50 mm. Five centimeters is roughly the width of three adult fingers held together, or the depth of a standard USB port slot.
Sources
References & further reading
- Bureau International des Poids et Mesures (BIPM) — The International System of Units (SI) — defines the metre and its prefixes centi- and milli-
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI)
- ISO 216:2007 — Paper sizes, defining A4 as 210 mm × 297 mm
- ISO/IEC 7810:2019 — Identification cards physical characteristics, defining ID-1 as 85.6 mm × 53.98 mm
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Shakeel Muzaffar is the Founder and Editor-in-Chief of MultiCalculators.com, bringing over 15 years of experience in digital publishing, product strategy, and online tool development. He leads the platform's editorial vision, ensuring every calculator meets strict standards for accuracy, usability, and real-world value. Shakeel personally oversees content quality, formula verification workflows, and the platform's commitment to publishing tools that are genuinely useful for students, professionals, and everyday users worldwide.
