How to Convert CM to Inches (Formula, Chart & Examples)
One inch is defined as exactly 2.54 centimeters — not approximately, but by international definition since 1959. That single number is all you need for every conversion between the two units.
The formula
inches = centimeters ÷ 2.54
And in reverse: centimeters = inches × 2.54
Examples:
- 30 cm ÷ 2.54 = 11.81 inches
- 170 cm ÷ 2.54 = 66.93 inches (5 ft 6.9 in)
- 21.5 in × 2.54 = 54.61 cm
For instant results with any value, use our CM to Inches Converter — it shows the answer as you type, along with a full conversion table.
CM to inches chart
| Centimeters | Inches |
|---|---|
| 1 cm | 0.39 in |
| 5 cm | 1.97 in |
| 10 cm | 3.94 in |
| 15 cm | 5.91 in |
| 20 cm | 7.87 in |
| 25 cm | 9.84 in |
| 30 cm | 11.81 in |
| 50 cm | 19.69 in |
| 100 cm | 39.37 in |
| 180 cm | 70.87 in |
Mental math tricks
You rarely need decimal precision in daily life. Two quick approximations:
- Divide by 2.5. Close enough for rough estimates: 25 cm ≈ 10 inches. This overestimates slightly (the true answer is 9.84”).
- The 4-to-10 rule. 10 cm ≈ 4 inches. So 30 cm ≈ 12 inches, 50 cm ≈ 20 inches. Easy to chain and accurate within 2%.
For height specifically: 5 feet = 152.4 cm, and each additional inch adds 2.54 cm. So 5’10” = 152.4 + 25.4 = 177.8 cm.
Where you’ll need this conversion
- Screen sizes are quoted in inches worldwide (a 15.6” laptop screen is 39.6 cm diagonal).
- Clothing — waist sizes in inches (a 32” waist is 81 cm).
- Height — converting between metric medical records and feet/inches.
- Furniture and DIY — US lumber and hardware specs are imperial; most of the world’s tape measures are metric.
Frequently asked questions
How many inches is 1 cm? 1 cm = 0.3937 inches — a bit less than half an inch.
Is 30 cm exactly 12 inches? No — 30 cm is 11.81 inches. A “30 cm ruler” and a “12 inch ruler” differ by about half a centimeter.
Why 2.54 exactly? In 1959 the inch was legally redefined in metric terms to standardize measurements internationally, and 2.54 cm was chosen as the exact value.
Convert any measurement instantly with the CM to Inches Converter, the reverse Inches to CM Converter, or the all-in-one Unit Converter for length, weight and temperature.