Softonic

CM to Inches Converter

Step 1 / 4 Centimeters to inches

1 inch equals exactly 2.54 centimetres — the relationship is defined by international agreement, not an approximation. Enter centimetres and the converter returns inches in decimal and optional fractional form (nearest 1/16 or 1/32, useful for woodworking and sewing). Works for anything: screen sizes, fabric, picture frames, construction, clothing measurements.

How cm to inches conversion works

  1. 1

    Enter cm

    Any decimal value. Strip the "cm" if pasted; the tool parses numbers only.

  2. 2

    Divide by 2.54

    Inches (decimal) = cm / 2.54.

  3. 3

    Optional fraction conversion

    Decimal inches round to nearest 1/2, 1/4, 1/8, 1/16 or 1/32 depending on the precision you need.

  4. 4

    Copy the result

    Decimal or fractional form. Paste into design software or a shopping form as needed.

Common values

cm Decimal inches Nearest 1/16 inch
1 0.394 6/16 (3/8)
2.54 1 1 exact
5 1.969 1 15/16
10 3.937 3 15/16
15 5.906 5 15/16
20 7.874 7 7/8
25 9.843 9 13/16
30 11.811 11 13/16
50 19.685 19 11/16
100 39.370 39 3/8

Key conversions to memorise

  • 1 inch = 2.54 cm
  • 10 cm ≈ 4 inches (actually 3.94)
  • 1 foot (12 inches) = 30.48 cm
  • 1 yard (3 feet) = 91.44 cm
  • 1 metre ≈ 39.37 inches ≈ 3.28 feet

When to use fractions vs decimals

  • Construction and woodworking (US): fractions to 1/16 or 1/32 inch. Tape measures and saw blades are marked this way.
  • Sewing (US): typically 1/8 inch precision.
  • Engineering / CAD: decimal inches, typically 3 decimal places.
  • Metric everywhere: decimals with the appropriate precision (0.5 mm for mechanical parts, 1 mm for furniture, 1 cm for rough measurements).
  • Screen sizes: decimal inches (“a 15.6-inch laptop”) or centimetres (“65-inch TV = 165 cm”).

Mental arithmetic

  • Divide cm by 2.5 for a fast approximation. 20 cm / 2.5 = 8 inches (actual 7.87). Easier than /2.54.
  • 10% shortcut: multiply cm by 0.4. 30 cm × 0.4 = 12 inches (actual 11.81).
  • For small values, remember that 1 cm is just under 0.4 inch — so anything under 10 cm is under 4 inches.
  • For large values, 100 cm = 39.37 inches ≈ 3 feet 3 inches.

Precision notes

  • The tool uses 2.54 exactly (no rounding in the conversion itself).
  • Display precision defaults to 2 decimal places for decimal inches, 1/16 for fractional.
  • For scientific work where more digits matter, bump the display precision up; internal math always carries full floating-point precision.

Frequently Asked Questions

Exactly. The international inch was defined as 25.4 mm exactly by the US and Commonwealth countries in 1959 — no approximation. Every conversion between cm and inches uses this exact factor.

Pre-1959, the US survey inch was very slightly different (factor of 2.5400050800…). For any modern measurement, 2.54 is exact. Only US geodetic surveys still occasionally reference the older value.

1/16 inch = 1.5875 mm. 1/32 inch = 0.7938 mm. Fine enough for most woodworking, sewing and general construction. Machining and engineering use decimal inches or direct metric.

Yes — useful for temperature differences or offsets. -5 cm → -1.97 inches. Not meaningful for physical dimensions but sometimes appears in measurement deltas.

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