Convert mm to inches
PrintMillimeter to Inch Conversion Table
| Millimeter (mm) | Inch (in) |
|---|---|
| 0.01 mm | 0.0003937008 in |
| 0.1 mm | 0.0039370079 in |
| 1 mm | 0.0393700787 in |
| 2 mm | 0.0787401575 in |
| 3 mm | 0.1181102362 in |
| 5 mm | 0.1968503937 in |
| 10 mm | 0.3937007874 in |
| 20 mm | 0.7874015748 in |
| 50 mm | 1.968503937 in |
| 100 mm | 3.937007874 in |
| 1000 mm | 39.37007874 in |
Millimeters and inches are the primary units used to specify fine measurements in engineering, 3D printing, mechanical machining, jewelry design, architecture, and tool manufacturing. While the millimeter (mm) is the standard metric subunit (1/1,000th of a meter) used worldwide, the inch (in) remains the primary measurement unit in the United States and Canada for hardware, lumber, and screen displays.
Our free online Mm to Inches Converter provides instant, high-precision length conversions in both directions:
- Millimeters to Inches: Multiply millimeters by
0.03937008(or divide by25.4). - Inches to Millimeters: Multiply inches by
25.4(exact international standard).
Exact Conversion Formulas: Millimeters & Inches
Since the International Yard and Pound Agreement of 1959, one inch is defined as exactly 25.4 millimeters. This establishes exact mathematical relationships:
| Conversion Direction | Exact Mathematical Formula | Quick Mental Approximation Rule |
|---|---|---|
| Millimeters to Inches | Inches = Millimeters ÷ 25.4 |
Divide mm by 25 (e.g., 50 mm ÷ 25 = 2 inches). |
| Inches to Millimeters | Millimeters = Inches × 25.4 |
Multiply inches by 25 (e.g., 2 inches × 25 = 50 mm). |
Step-by-Step Calculation Example
To convert 15 millimeters to inches:
15 mm ÷ 25.4 = 0.590551 inches (or 15 × 0.03937008 = 0.590551 in)
Thus, 15 millimeters is equivalent to approximately 0.591 inches (slightly over 9/16 of an inch).
Millimeter to Inch Conversion Table
Below is a precision reference lookup table for converting common hardware and engineering measurements from 0.01 mm up to 1,000 mm:
| Millimeters (mm) | Exact Equivalent in Inches (in) | Common Engineering Benchmark |
|---|---|---|
| 0.01 mm | 0.00039370 in | Precision machining tolerance (10 microns) |
| 0.1 mm | 0.00393701 in | Average thickness of a sheet of paper |
| 0.4 mm | 0.01574803 in | Standard 3D printer nozzle diameter |
| 1.0 mm | 0.03937008 in | Thickness of a standard credit card |
| 2.0 mm | 0.07874016 in | Small mechanical screw thread pitch |
| 5.0 mm | 0.19685039 in | M5 machine bolt diameter (~3/16 in) |
| 10.0 mm (1 cm) | 0.39370079 in | 10 mm socket wrench benchmark (~3/8 in) |
| 20.0 mm | 0.78740157 in | 20 mm camera lens focal step |
| 25.4 mm (1 Inch Exact) | 1.00000000 in | 1.0 Inch Exact International Standard |
| 50.0 mm | 1.96850394 in | 50 mm standard camera prime lens (~2 inches) |
| 100.0 mm | 3.93700787 in | 10 cm / 4-inch pipe benchmark |
| 1,000.0 mm (1 Meter) | 39.37007874 in | 1 Meter = 39.37 inches (3.28 feet) |
History & Scientific Definition: Millimeter vs. Inch
The Definition of the Millimeter (mm)
The millimeter is a submultiple of the meter in the International System of Units (SI). Combining the prefix milli- (from Latin mille meaning thousandth), 1 mm equals 1/1,000th of a meter. Under modern SI quantum definitions, 1 millimeter is officially defined as the exact distance traveled by light in a vacuum during 1 / 299,792,458,000th of a second.
The Definition of the Inch (in)
Derived from the Roman uncia (1/12th of a Roman foot), the inch was historically measured using natural objects like three dry barleycorns laid end-to-end or the average width of human thumbs. In 1959, international standards bureaus locked the inch to the metric system, defining 1 inch as exactly 25.4 mm.
To convert larger metric lengths, use our Cm to Inches Converter. For tile and building construction measurements, visit our Tile Calculator. For general unit transformations across length, volume, and mass, explore our Conversion Calculator.
Frequently Asked Questions (FAQ)
How many millimeters are in 1 inch?
There are exactly 25.4 millimeters in 1 inch.
How many inches are in 1 millimeter?
There are approximately 0.0393701 inches in 1 millimeter (1 ÷ 25.4).
What is a 10 mm socket wrench size in fractional inches?
A 10 mm socket measures 10 ÷ 25.4 = 0.3937 inches. This is extremely close to a 3/8 inch socket (0.375 inches) or a 13/32 inch socket (0.406 inches).
How do I convert fractional inches (like 1/4 inch or 1/2 inch) to mm?
Convert the fraction to a decimal first, then multiply by 25.4:
- 1/4 inch =
0.25 × 25.4 = 6.35 mm - 1/2 inch =
0.50 × 25.4 = 12.70 mm - 3/4 inch =
0.75 × 25.4 = 19.05 mm