Inches to Centimeters: Complete Conversion Guide

4 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

Inches and centimeters are the everyday units for measuring smaller lengths — screen sizes, waist measurements, paper sizes, and hardware dimensions. The conversion factor, 2.54, is exact by international definition and is one of the most useful numbers to memorize.

Whether you're buying a 55-inch TV and want to know if it fits, converting a clothing measurement, or reading a technical spec sheet, this guide covers everything you need.

The Conversion Formula

centimeters = inches × 2.54  (exact)

inches = centimeters ÷ 2.54  (exact)

Examples:
  1 in  ×  2.54 =   2.54 cm
  6 in  ×  2.54 =  15.24 cm
 12 in  ×  2.54 =  30.48 cm  (= 1 foot)
 55 in  ×  2.54 = 139.70 cm  (55-inch TV screen diagonal)

Why Is 2.54 Exact?

Since 1959 the inch has been defined as exactly 2.54 centimeters under the International Yard and Pound Agreement, signed by the US, UK, Canada, Australia, New Zealand, and South Africa. This means there is no approximation in the conversion factor — 2.54 is definitional, not measured.

Before 1959, the US and UK used slightly different inch definitions, which caused minor discrepancies in engineering projects. The 1959 agreement eliminated this ambiguity, making transatlantic manufacturing tolerances unambiguous.

Quick Conversion Tips

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Multiply inches by 2.5 for a fast estimate — accurate to within 1.6%.
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To go the other way (cm → in), divide by 2.54 or multiply by 0.394.
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Screen sizes are always diagonal in inches: a '55-inch' TV is 139.7 cm diagonally.
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Common anchor: 1 foot (12 inches) = 30.48 cm ≈ 30 cm for quick estimates.
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For body measurements: 1 inch of waist ≈ 2.5 cm is precise enough for sizing.

Frequently Asked Questions

How many cm is 5 inches?

5 inches equals exactly 12.7 centimeters. The calculation: 5 × 2.54 = 12.7 cm.

How many inches is 30 cm?

30 cm equals approximately 11.81 inches. A standard 12-inch ruler is 30.48 cm — so 30 cm is just a hair under 12 inches.

How many cm is 1 inch?

1 inch equals exactly 2.54 centimeters by international definition. This is the single most useful conversion factor to memorize for length.

Is a centimeter bigger than an inch?

No. One inch equals 2.54 centimeters, making an inch larger. If you're reading a measurement in centimeters and want it in inches, the number will get smaller when you divide by 2.54.

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