cm to mm Converter

What centimeters and millimeters are used for

Centimeters (cm) and millimeters (mm) are metric units of length used for everything from school measurements to engineering drawings. Centimeters are handy for everyday objects—phone sizes, notebook widths, furniture details—while millimeters are often used when precision matters, like material thickness, drill bits, mechanical parts, jewelry sizing, and technical specifications.

The simple rule: 1 cm equals 10 mm

This conversion is one of the easiest in the metric system:

Because this is a fixed base-10 relationship, converting between cm and mm is exact. All you’re doing is shifting the decimal point.

How to convert cm to mm

To convert centimeters to millimeters, multiply by 10:

Example: whole centimeters

7 cm × 10 = 70 mm.

Example: decimal centimeters

2.35 cm × 10 = 23.5 mm. Decimals are common when reading calipers or detailed specs.

How to convert mm to cm

To convert millimeters to centimeters, divide by 10:

Example: 25 mm

25 mm ÷ 10 = 2.5 cm.

Where this conversion shows up in real life

Construction, home projects, and materials

Many materials list thickness in mm (tile, glass, plywood, sheet metal) while room or object dimensions might be in cm. Converting between them helps you compare sizes quickly and avoid ordering the wrong thickness or clearance.

Engineering drawings and technical specs

Technical drawings often use mm by default because it reduces decimals. A part might be 120 mm long rather than 12.0 cm. Converting can help when you need a more familiar unit for a quick mental picture.

DIY tools and measurement devices

Some tape measures and rulers show cm and mm together. When you see 13.7 cm on a tape, you’re already reading the mm component (137 mm). A converter is useful when you’re transferring measurements into a spreadsheet or ordering parts online.

Schoolwork and math practice

cm↔mm conversions are common in early geometry and measurement problems. Knowing the “×10” and “÷10” rule makes these questions quick and helps reduce careless mistakes.

Rounding and precision

When you don’t need decimals

If your input is a whole number of centimeters, your output in millimeters is always a whole number too. In these cases, rounding doesn’t matter.

When decimals matter

If your input has decimals, your mm output might also have decimals. For example, 0.05 cm = 0.5 mm. If your measurement tool can only read to the nearest 1 mm, rounding can make the output match your real-world precision.

Pick a rounding direction for your situation

• Round: best for general use.
• Round down: useful when you must not exceed a limit (like a clearance).
• Round up: useful when you want to avoid underestimating (like a minimum thickness).

Quick reference conversions

• 0.1 cm = 1 mm
• 0.5 cm = 5 mm
• 1 cm = 10 mm
• 2 cm = 20 mm
• 5 cm = 50 mm
• 10 cm = 100 mm
• 15 cm = 150 mm
• 20 cm = 200 mm

Common mistakes this converter prevents

• Moving the decimal the wrong way: cm→mm is ×10, mm→cm is ÷10.
• Mixing cm/mm with inches: mm and cm are metric; inches are imperial and use a different factor (25.4 mm per inch).
• Rounding too early: keep full precision through your calculations, then round once at the end.

A simple mental check

A good sanity check is to remember that millimeters are smaller than centimeters. So the number should get bigger when you convert cm to mm. If it gets smaller, the decimal moved the wrong way.