How many millimeters are in one inch?
One inch is exactly 25.4 millimeters.
Convert Inch (in) to Millimeter (mm) instantly.
Choose how you want the answer displayed.
1in=25.4mm
| Quick Conversion | Converted |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 6 in | 152.4 mm |
| 12 in | 304.8 mm |
| 24 in | 609.6 mm |
| 36 in | 914.4 mm |
| 60 in | 1,524 mm |
| 72 in | 1,828.8 mm |
An inch (in or ") is a customary and imperial unit of length.
One inch is equal to 1/12 of a foot (ft), 1/36 of a yard (yd), and exactly 2.54 centimeters (cm).
Same length, two labels
1 in = 25.4 mm
A millimeter is a metric length unit equal to one thousandth of a meter.
Millimeters are used for detailed measurement in engineering, product design, medicine, and manufacturing.
Mathematically, millimeter (mm) = inch (in or ") multiplied by the conversion factor shown below.
1 in = 25.4 mm
1 mm = 0.03937 in
1 in x 25.4 = 25.4 mm
The distance in millimeter (mm) is the distance in inch (in or ") multiplied by 25.4.
distance(mm) = distance(in) x 25.4
Or:
mm = in x 25.4
Formula: value × 25.4
Example: 15 in = 381 mm
Convert 8 inch to millimeter:
8 in x 25.4 = 203.2 mm
Convert 24 inch to millimeter:
24 in x 25.4 = 609.6 mm
Precision note: Use 1 in = 25.4 mm exactly. Avoid rounding early when the result affects fit, tolerance, or compatibility.
1 in = 25.4 mm
1 mm = 0.03937 in
If you are starting with millimeter instead, use the mm to inches page.
| Inch [in] | Millimeter [mm] |
|---|---|
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 8 in | 203.2 mm |
| 10 in | 254 mm |
| 18 in | 457.2 mm |
| 30 in | 762 mm |
| 48 in | 1,219.2 mm |
| 96 in | 2,438.4 mm |
| 120 in | 3,048 mm |
| 144 in | 3,657.6 mm |
One inch is exactly 25.4 millimeters.
0.5 inches is exactly 12.7 millimeters.
For casual display, rounding is fine. For fit, hardware, or technical work, keep the exact decimal result until the final specification.