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Convert in to mm

A practical reference for converting inches (in) to millimeters (mm), a length unit. Type any value for an instant result, or use the reference table below.

1 in = 25.4 mm
mm = in × 25.4
25.4 mm

Conversion formula

mm = in × 25.4

Multiply inches by 25.4. Useful for tool and hardware sizing.

Quick reference table

inchesmillimeters
1 in25.4 mm
2 in50.8 mm
3 in76.2 mm
4 in101.6 mm
5 in127 mm
6 in152.4 mm
8 in203.2 mm
10 in254 mm
12 in304.8 mm
20 in508 mm

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Frequently asked questions

How many mm is 1 in?

1 in equals 25.4 mm.

Why does my result differ slightly from other sites?

Rounding. This page displays four decimal places while the underlying calculation keeps full precision.

Is my input sent to a server?

No. Every calculation runs locally in your browser and nothing is transmitted.

All calculations on this page run in your browser. Your input is never sent to a server.

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