Inches to Millimeters
Inches to millimeters converter: multiply by 25.4 (1 in = 25.4 mm). Includes a reference table, sample calculations and the inverse ratio 0.03937.
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How inches convert to millimeters
This page converts inches (in) to millimeters (mm). In the converter's unit table, one inch equals 25.4 millimeters, so every result here comes from a single multiplication by 25.4.
The ratio works in both directions: multiply by 25.4 to go from inches to millimeters, or multiply by 0.039370079 to go from millimeters back to inches.
Quick lookup: inches in millimeters
A set of 12 in amounts is converted to mm below, using the same function as the converter at the top of the page.
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.25 | 6.35 |
| 1 | 25.4 |
| 1.5 | 38.1 |
| 3 | 76.2 |
| 6 | 152.4 |
| 8 | 203.2 |
| 15 | 381 |
| 40 | 1,016 |
| 75 | 1,905 |
| 150 | 3,810 |
| 400 | 10,160 |
| 2,000 | 50,800 |
Values in the mm column are shown the way the converter shows them, with a limited number of significant digits.
Worked examples for inches to millimeters
Convert 8.5 in first. Using 25.4 as the multiplier, the answer displayed is 215.9 mm.
Take 0.55 inches as the second case. The widget returns 13.97 millimeters, and that figure divided by 25.4 returns to about 0.55.
Working backwards, an amount of 6,500 mm corresponds to 255.9055118 in.
The reverse: millimeters to inches
To start from millimeters instead, open Millimeters to Inches. For that direction 1 mm = 0.039370079 in, and its reference table is built around millimeters as the input.
For other combinations, the Length Converter offers every unit in one pair of dropdowns.
Other conversions in this family
These pages cover neighbouring unit pairs from the same converter.
Frequently asked questions
How many mm make up 1 in?
One inch equals 25.4 millimeters. The relationship is linear, so 10 in is 254 mm and 100 in is 2,540 mm.
What is 1 mm in in?
There are 0.039370079 inches in one millimeter. That is the inverse of 25.4, and 10 millimeters come to 0.39370079 inches.
How do I convert 2.4 in to mm?
Using 25.4 as the multiplier, 2.4 inches equals 60.96 millimeters.
How does the converter round results?
The widget calculates with ordinary floating-point numbers and only rounds what it displays. Results of 1 or more show up to 10 significant digits, results below 1 show up to 8, and results from 1,000 upward show up to 6 decimal places with thousands separators. As an example, 0.123456789 in displays as 3.135802441 mm and 1,234.5678 in displays as 31,358.02212 mm.
Where does the in to mm result come from?
Behind the scenes, inches and millimeters are each tied to the same base unit by a stored factor. The ratio of those factors, 25.4, is what turns an in value into a mm value.
What is the reverse of in to mm?
Reversing the pair: multiply by 0.039370079, or equivalently divide by 25.4. The page titled "Millimeters to Inches" covers it, or you can press the swap button in the widget above. Example: 25 mm = 0.98425197 in.
Learn more from an authoritative source:
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