Convert MM to Inches

Convert millimetres to inches for engineering and DIY.

MM to Inches Converter

Universal unit converter engine

Conversion Category

From Value

Converted Result

Conversion Formula1 nm = 0.001 µm

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What does MM to Inches Converter do?

Convert millimetres to inches exactly, with fractional output to the nearest 64th for precision engineering. Also converts in reverse and shows the decimal thou (thousandths of an inch) used in machining.

How to Use MM to Inches Converter

1
Enter a value in millimetresDecimals welcome.
2
Choose the fraction precision64ths for engineering, 16ths for DIY.
3
Read the resultDecimal, fraction and thou.

Key Features

Exact conversion: 1 inch = 25.4 mm
Fractions to the nearest 64th, 32nd, 16th or 8th
Thou (thousandths of an inch) for machining
Two-way conversion in one tool
Reference table including common drill and fastener sizes

Frequently Asked Questions

How many mm is 1 inch?

Exactly 25.4 mm. Every other imperial length derives from this definition, which is what makes the conversions exact rather than approximate.

What is a thou?

One thousandth of an inch, 0.0254 mm, also called a mil. It is the standard precision unit in machining and PCB design, where tolerances are quoted in thou.

Why round to 64ths?

Because imperial tooling comes in binary fractions. Drill bits, wrenches and stock thicknesses are sized in 64ths, 32nds and 16ths, so the nearest fraction tells you which tool to reach for.

How many mm is a quarter inch?

6.35 mm exactly. A half inch is 12.7 mm and three quarters is 19.05 mm — all exact, since 25.4 divides cleanly.

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