Inches to MM converter

How to convert inches to millimeters

To convert inches to millimeters, use mm = in × 25.4. For example, 8 in is 203.2 mm. Type any value in the converter above and the result updates instantly.

The Inches to MM formula

The conversion is mm = in × 25.4. One inch equals 25.4 mm. This conversion is exact: inch is defined precisely in terms of millimeter, so the only rounding is in the digits shown.

Inches to MM conversion table

Where inches and millimeters are used

Inches are the standard for screen sizes, tires, pipes, paper and tool sizes everywhere, and for everyday lengths in the United States.

Millimeters are used for precise measurements: engineering, machining, photography (lens and sensor sizes) and hardware.

Worked examples

These examples use the formula above, so you can check the converter or do the same by hand:

• 2 in = 50.8 mm
• 4 in = 101.6 mm
• 6 in = 152.4 mm

Converting inches to millimeters in your head

As a quick estimate, multiply by 25 (rounded).

MM to Inches reference table

For the opposite direction, these values are handy to have at hand:

Common mistakes to avoid

• Do not confuse the international inch (exactly 25.4 mm) with the US survey foot used in old land records; everyday conversions use the international values.
• Feet and inches are often written together: 5 ft 9 in is 69 inches, or 175.26 cm.

About this converter

The converter accepts whole numbers, decimals and negative values, gives the result as you type, and uses full precision internally, so what you copy is as accurate as it can be. It runs in your browser: nothing you type is sent to a server, it keeps working offline once the page has loaded, and there is nothing to install.

Need the opposite direction? Use the MM to Inches converter.