Inches to Millimeters Converter
Convert inches to millimeters instantly with this free inches to millimeters converter. Enter any value to get an accurate length conversion, plus the formula, the conversion factor and a full reference table.
What is 1 inch in millimeters?
1 inch is equal to exactly 25.4 millimeters.
1 × 25.4 = 25.4 millimeters
1 inch = 25.4 millimeters
Inches to Millimeters formula
mm = in × 25.4
The inches to millimeters conversion factor is 25.4, which is exact by definition. 1 inch = 25.4 millimeters, and 1 millimeter = 0.03937007874 inches.
Worked examples
- 2 inches = 50.8 millimeters — 2 × 25.4 = 50.8 millimeters
- 6 inches = 152.4 millimeters — 6 × 25.4 = 152.4 millimeters
- 10 inches = 254 millimeters — 10 × 25.4 = 254 millimeters
Inches to Millimeters conversion table
Every value below is calculated with the exact conversion factor and rounded for display.
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| 12 in | 304.8 mm |
| 15 in | 381 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 30 in | 762 mm |
| 50 in | 1,270 mm |
| 75 in | 1,905 mm |
| 100 in | 2,540 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
When you need to convert inches to millimeters
- Buying furniture, TVs or appliances listed in one system and fitting them into a room measured in the other.
- Following building plans, sewing patterns or DIY instructions written abroad.
- Reading height, screen size or luggage limits when travelling between the US and the rest of the world.
Getting a feel for the scale
A converted number is easier to trust when you can picture it. These reference points let you sanity-check the result at a glance.
Inch (in)
- A US quarter is about 1 inch across
- Standard printer paper is 8.5 inches wide
Millimeter (mm)
- A credit card is 0.76 mm thick
- A UK 1p coin is about 1.5 mm thick
Common mistakes to avoid
- Dividing when you should multiply. Because 1 inch = 25.4 millimeters, the answer should be larger than the number you started with.
- Rounding too early. Convert first at full precision, then round the final answer to the precision the task actually needs.
How precise does the answer need to be?
For everyday measurements round to the nearest whole unit or to one decimal place. Machining, sewing and construction usually need at least two decimals — and it is worth measuring in the target unit directly when tolerance matters.
How these units are defined
- Inch (in): Exactly 25.4 millimeters; the base small unit of US customary and Imperial length. This unit's relationship to the SI base unit is exact by definition, so no rounding enters the conversion factor.
- Millimeter (mm): One thousandth of a meter; the standard fine unit on metric rulers. This unit's relationship to the SI base unit is exact by definition, so no rounding enters the conversion factor.
Related conversions
Frequently asked questions
- What is 1 inch in millimeters?
- 1 inch is equal to 25.4 millimeters.
- How many inches are in one millimeter?
- There are 0.039370079 inches in 1 millimeter.
- How do you convert inches to millimeters?
- Multiply the number of inches by 25.4 — or use the formula mm = in × 25.4.
- What is 6 inches in millimeters?
- 6 inches is 152.4 millimeters. 6 × 25.4 = 152.4 millimeters.
- Is the inches to millimeters conversion exact?
- Yes. The relationship is fixed by definition, so 25.4 is an exact conversion factor — only the displayed result is rounded.