Inches to Millimetres Converter
Convert inches to millimetres instantly. The calculator accepts decimals and common fractions — including mixed values such as 8 5/8. 1 inch = 25.4 millimetres exactly.
One inch is defined as exactly 25.4 millimetres. To convert inches to millimetres, multiply by 25.4. For fractional inches, first convert the fraction to a decimal (e.g. 5/8 = 0.625), then multiply.
How to convert inches to millimetres
Inches to millimetres conversion table
Frequently asked questions
How many millimetres are in an inch?
There are exactly 25.4 millimetres in one inch. This is the internationally agreed definition, used since 1959, so the conversion never changes.
How do I convert fractional inches to millimetres?
Convert the fraction to a decimal first (e.g. 5/8 = 0.625), then multiply by 25.4. Our calculator accepts fractions directly — type "5/8" or "8 5/8" and it does the rest.
What is 8 5/8 inches in millimetres?
8 5/8 inches equals 219.075 mm (8.625 × 25.4 = 219.075). See our dedicated 8 5/8 in mm page for the full breakdown.
What is half an inch in millimetres?
Half an inch (1/2 in) equals 12.7 mm (0.5 × 25.4 = 12.7). See our half inch to mm page for more detail.
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