Inches to centimetres (in to cm)

The formula

cm = in × 2.54

Where the factor comes from — each unit by its definition, then its size in SI:

• 1 in = 2.54 × cm = 0.0254 m
• 1 cm = m / 100 = 0.01 m

Dividing the two SI sizes gives the factor: 2.54, exact — every step above is a definition, not a measurement. The reverse factor is 0.393700787402.

Every formula on this site takes lengths in metres. Heights, distances and stopping distances quoted in feet, inches or miles have to be converted first — getting it wrong by a factor of 3.28 is the most common unit slip in homework.

Worked examples

• A sprint track straight (100 m): 3,937.01 in = 10,000 cm — 3,937.01 × 2.54 = 10,000
• A marathon (42.195 km): 1,661,220 in = 4,219,500 cm — 1,661,220 × 2.54 = 4,219,500
• A tall doorway (6 ft): 72 in = 182.88 cm — 72 × 2.54 = 182.88
• A school ruler: 11.811 in = 30 cm — 11.811 × 2.54 = 30

Frequently asked questions