Convert Inches to Millimeters
Convert Inches to Millimeters instantly. 1 Inch (in) equals 25.4 Millimeters (mm).
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 |
| 20 in | 508 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
1 Inch = 25.4 Millimeters · multiply Inches by 25.4
About converting Inches to Millimeters
Inches (in) and Millimeters (mm) are both units of length, so converting between them is a single multiplication: multiply your Inches figure by 25.4. Ten Inches comes to 254 Millimeters, and a hundred works out at 2,540 Millimeters.
Rule of thumb: going from Inches to Millimeters multiplies, so the figure always grows — one Inch is already 25.4 Millimeters. If your answer came out smaller, you have the conversion the wrong way round.
What is an Inch?
An inch is exactly 2.54 centimeters — a rare case where an imperial and a metric unit line up on a tidy number, because the inch was redefined in terms of the meter rather than the other way round. It has quietly outlived most imperial units by attaching itself to technology: screen sizes, wheel and tyre diameters, plumbing pipe, and screw threads are specified in inches worldwide, so even in thoroughly metric countries people buy a 15-inch laptop and 17-inch wheels.
What is a Millimeter?
A millimeter is one thousandth of a meter, and it is where metric measurement starts getting genuinely precise. It is the working unit of engineering drawings, machine shops, rainfall figures and camera lenses — a "50 mm lens" and "12 mm of rain overnight" are both millimeter measurements. Technical drawings in most of the world default to millimeters precisely because it lets a draughtsman specify a whole component without ever writing a decimal point.
To put both in perspective: an inch is about the width of an adult thumb, while a credit card is about 0.76 millimeters thick.
The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Millimeters to Inches converter, or browse all Length converters.
Frequently asked questions
How many Millimeters are in one Inch?
There are 25.4 Millimeters in one Inch.
How do I convert Inches to Millimeters?
Multiply the number of Inches by 25.4. For example, 10 Inches = 254 Millimeters.
What is 100 Inches in Millimeters?
100 Inches is equal to 2,540 Millimeters.
How do I convert Millimeters to Inches?
Multiply the Millimeters value by 0.03937 (or divide by 25.4).
Is this Inches to Millimeters conversion exact?
Yes, exactly. Both units are fixed against the same base by definition, and 1 Inch = 25.4 Millimeters is the complete value — nothing is rounded away.
What is an Inch?
An inch is exactly 2.54 centimeters — a rare case where an imperial and a metric unit line up on a tidy number, because the inch was redefined in terms of the meter rather than the other way round. It has quietly outlived most imperial units by attaching itself to technology: screen sizes, wheel and tyre diameters, plumbing pipe, and screw threads are specified in inches worldwide, so even in thoroughly metric countries people buy a 15-inch laptop and 17-inch wheels.
What is a Millimeter?
A millimeter is one thousandth of a meter, and it is where metric measurement starts getting genuinely precise. It is the working unit of engineering drawings, machine shops, rainfall figures and camera lenses — a "50 mm lens" and "12 mm of rain overnight" are both millimeter measurements. Technical drawings in most of the world default to millimeters precisely because it lets a draughtsman specify a whole component without ever writing a decimal point.