inches to millimeters Converter
Type a value in inches and get the answer in millimeters instantly — or convert the other way. The conversion uses the exact relationship 1 inches = 25.4 millimeters, the same formula used in textbooks and engineering references.
Precision work — drill bits, camera mounts, 3D printing, jewelry — lives in millimeters, while US tools and hardware still speak inches. One inch is officially exactly 25.4 millimeters, so this conversion is precise to any decimal place.
How to use
- Type your value into the inches box — the millimeters result updates as you type.
- To go the other direction, type into the millimeters box instead and read the inches result.
- Copy the result with one tap, or scan the reference table below for common values.
Frequently asked questions
How do you convert inches to millimeters?
Multiply the number of inches by 25.4. For example, 10 inches = 254 millimeters. The converter above does this for you and shows more decimal places than you will ever need.
How many millimeters are in one inches?
Exactly 25.4 millimeters. This is a fixed definition, not an approximation, so the conversion is exact at any scale.
Is this converter accurate for professional use?
Yes — it uses full double-precision arithmetic and the official inches-to-millimeters factor, so results are reliable for schoolwork, cooking, fitness, travel and technical work.
Can I convert millimeters back to inches?
Yes. The converter is two-way: just type in the second box and the first box updates instantly with the reverse conversion.