ConvBolt — Unit ConverterInches to Millimeters Converter
Converting inches to millimeters is a multiplication by a fixed factor: 1 in = 25.4 mm. The table below covers the values people look up most often, and the formula section shows exactly where that factor comes from.
Because one inch works out to 25.4 mm, the millimeter is the noticeably larger unit of the two: a figure given in millimeter always carries a larger number than the same measurement in inch. A chart drawn in in can hide that, so check which label the axis uses before you compare two readings.
DIY and home-improvement work is where this pair shows up most: you measure in inches but the hardware store or an imported product sheet quotes millimeters, so the conversion has to be right the first time.
The conversion factor used here is 25.4 mm per inch (1 significant digits as shown). Kept to seven figures it covers professional measurement; if you round it to two or three decimals for a spreadsheet, the error scales with the input — at a value of 1,000 in a factor rounded to three decimals can be off by a measurable amount. The reverse direction uses 0.03937008 in per mm, the exact reciprocal, so a round trip through both pages returns your original number.
Inches to Millimeters formula
Use this formula to convert any inch value to millimeters:
Worked example: 100 in × 25.4 = 2540 mm.
Inches to Millimeters conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 500 in | 12700 mm |
| 1000 in | 25400 mm |
How to convert inches to millimeters
Multiply the inch value by 25.4 to get the equivalent in millimeters. This single factor works for every value in the table above and for anything else you need — there is no per-value adjustment, which is why a conversion table and a calculator always agree.
If you need the opposite direction, use the Millimeters to Inches converter instead of dividing by hand; both pages use the same source factors. For every other in conversion in one place, see the in conversion hub.
Frequently asked questions
How many millimeters are in 1 inch?
1 inch = 25.4 mm.
What is 100 inches in millimeters?
100 in = 2540 mm.
Is converting inches to millimeters the same as millimeters to inches?
No — the direction changes the multiplier. The reverse conversion (1 mm = 0.03937008 in) is on the Millimeters to Inches page.
Related conversions
Try the ConvBolt Unit Converter for any other length unit, browse the Length conversions, or read our conversion guides.