LumberCalcs: The Straight-Grain Figures for the Hand-Hewn Builder

Millimeters to Inches Converter

Millimeters to Inches: both directions, instantly.

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Millimeters to Inches Converter

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25.4 mm per inch, exactly

Since 1 inch is exactly 2.54 cm, and 1 cm is 10 mm, 1 inch is exactly 25.4 mm -- an exact, defined conversion, not an approximation.

Where metric shows up in lumber work

Most US lumber is sold and measured in inches and feet, but you'll run into millimeters when working with imported hardware, European-made tools, metric plywood thicknesses, or imported furniture hardware and hinges that specify hole spacing and dimensions in mm. This converter handles length both directions.

The mm-to-inch relationship is an exact, internationally defined conversion (1 inch = 25.4 mm exactly), not an approximation.

Frequently asked questions

Is 25.4 mm per inch exact or rounded?

Exact -- the inch has been internationally defined as exactly 25.4 millimeters since 1959, so this conversion carries no rounding error.

Why would a lumber project need millimeters?

Imported hardware, hinges, European tool measurements, and some imported sheet goods commonly specify dimensions in millimeters even when the rest of a US project uses inches and feet.

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