CM to Inches Converter
Convert centimetres to inches and inches back to centimetres.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
1 in = 2.54 cm
About this calculator
One inch is exactly 2.54 centimetres, so the conversion is exact in both directions. This is one of the most frequently needed conversions for clothing, screens and furniture.
Worked example
calculated with the default values below
Value 30 · Direction Direction · Decimal places 4 · From Centimetres (cm) · To Inches (in) Result 11.811 · In feet and inches 0 ft 11.8 in · In metres 0.3 m
Method and assumptions
Formula basis and scope
1 in = 2.54 cm.
Only the displayed unit definitions are converted; rounding and measurement uncertainty are separate.
Data sources
Disclaimer
These calculators give general conversion results. Rounding and the precision of the value you enter both affect the output, so treat displayed decimals as indicative rather than exact.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
in = cm ÷ 2.54; cm = in × 2.54
- cm
- length in centimetres
- in
- length in inches
1 inch is exactly 2.54 cm; the metres output is cm ÷ 100.
Frequently asked questions
Is the inch defined exactly, or is it an approximation?
Exactly. Since 1959 an inch has been defined as precisely 25.4 millimetres by international agreement, so no accuracy is lost in the conversion. Any apparent rounding is in the display, not the definition. This is why inch-to-millimetre conversions can be treated as exact arithmetic rather than as estimates.
Why do some tools give a slightly different answer?
Because they round at different points. Converting centimetres to inches and back, or rounding to two decimal places between the two steps, accumulates a small error. Doing the whole calculation in one step and rounding only the final display avoids it. For any chain of conversions, keep full precision internally and round once at the end.