Inches to Millimeters
Convert inches to millimeters instantly, with a reference table.
Inches to Millimeters at a glance
Inches to Millimeters is a free online converter you can use right now to convert inches to millimeters instantly, with a reference table โ no account, no install and no usage limit. It runs entirely inside your browser, so whatever you enter stays on your own device.
- Price
- Free โ no trial, no paid tier, no watermark
- Sign-up
- Not required
- Where it runs
- In your browser โ nothing is uploaded to a server
- Works on
- Chrome, Safari, Firefox and Edge โ desktop, tablet and phone
- Category
- Unit Conversions
Inches to Millimeters conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 500 in | 12,700 mm |
| 1000 in | 25,400 mm |
About Inches to Millimeters
Convert inches to millimeters instantly, with a reference table of common values. The factor is exact: 1 in = 25.4 mm.
Machining and fabrication work in millimetres, so an imperial dimension from a drawing or a hardware spec usually has to come across to millimetres before anything can be cut or drilled.
The inch began as the width of a thumb and was standardised in 1959, when the international yard and pound agreement defined it as exactly 2.54 centimetres. That figure is a definition, not a rounded measurement. It remains standard in the United States and persists worldwide for screen and display sizes, pipe and tyre diameters, and print dimensions regardless of the local system. A standard sheet of US Letter paper is 8.5 inches wide, and a typical laptop screen is 13 to 15 inches measured diagonally.
Worked through with real numbers: 1 in is 25.4 mm, 10 in is 254 mm, 100 in is 2540 mm.
As for the other side of the conversion: A credit card is 0.76 mm thick and a standard pencil lead is 0.7 mm across.
Length conversions between metric and imperial are exact by definition rather than approximate. The 1959 international yard and pound agreement fixed the inch at precisely 2.54 cm and the yard at 0.9144 m, so these factors are definitions and carry no measurement error.
How to use Inches to Millimeters
- Enter the number of inches you want to convert.
- The equivalent in millimeters appears instantly โ there is no button to press.
- Check the reference table for common Inches to Millimeters values.
Frequently asked questions
How do I convert inches to millimeters?
Multiply your inches figure by 25.4 to get millimeters โ or type a value above and read the answer straight off.
How many millimeters are in one inche?
1 in = 25.4 mm.
When would I need to convert inches to millimeters?
Machining and fabrication work in millimetres, so an imperial dimension from a drawing or a hardware spec usually has to come across to millimetres before anything can be cut or drilled.
What is a inche, exactly?
The inch began as the width of a thumb and was standardised in 1959, when the international yard and pound agreement defined it as exactly 2.54 centimetres. That figure is a definition, not a rounded measurement. A standard sheet of US Letter paper is 8.5 inches wide, and a typical laptop screen is 13 to 15 inches measured diagonally.
Where is the millimeter actually used?
It is the working unit of engineering drawings, machining and construction, where specifying in centimetres would introduce ambiguous decimal places. Technical drawings almost universally use millimetres without stating the unit. A credit card is 0.76 mm thick and a standard pencil lead is 0.7 mm across.
Is there anything tricky about length conversions?
Length conversions between metric and imperial are exact by definition rather than approximate. The 1959 international yard and pound agreement fixed the inch at precisely 2.54 cm and the yard at 0.9144 m, so these factors are definitions and carry no measurement error.
Is this converter accurate?
Yes. It uses the exact standard factor of 1 in = 25.4 mm, and the conversion runs in your browser so nothing is uploaded.