Millimeters to Inches Converter
Enter the length in millimeters below to convert it to inches.
Convert Millimeters to Inches
Enter a value in millimeters (mm) to convert to inches (in).
Millimeters to Inches Conversion Chart (1–40 Continuous)
Continuous 1 to 40 millimeters lookup table with exact decimals and reduced nearest 1/64 fractions. Highlighted rows mark common shop and ruler values.
| Millimeters (mm) | Decimal (in) | Fraction — Nearest 1/64 (Reduced) | Nearest 1/16 (Tape) |
|---|---|---|---|
1 mm★ Common | 0.03937 in | 3/64 in | 1/16 in |
2 mm★ Common | 0.07874 in | 5/64 in | 1/16 in |
3 mm★ Common | 0.11811 in | 1/8 in | 1/8 in |
4 mm | 0.15748 in | 5/32 in | 3/16 in |
5 mm★ Common | 0.19685 in | 13/64 in | 3/16 in |
6 mm★ Common | 0.23622 in | 15/64 in | 1/4 in |
7 mm | 0.275591 in | 9/32 in | 1/4 in |
8 mm★ Common | 0.314961 in | 5/16 in | 5/16 in |
9 mm | 0.354331 in | 23/64 in | 3/8 in |
10 mm★ Common | 0.393701 in | 25/64 in | 3/8 in |
11 mm | 0.433071 in | 7/16 in | 7/16 in |
12 mm★ Common | 0.472441 in | 15/32 in | 1/2 in |
How to Convert Millimeters to Inches
To convert millimeters to inches, multiply the length by the following conversion ratio: 0.0393701 inches/millimeter.
Since one millimeter is equal to 0.0393701 inches, you can use this simple formula to convert:
The length in inches is equal to the length in millimeters multiplied by 0.0393701.
For example, here's how to convert 15 millimeters to inches using the formula above.
How Many Inches Are in a Millimeter?
There are 0.0393701 inches in a millimeter, which is why we use this value in the formula above.
Our millimeter fraction and decimal calculator can convert millimeters and inches, and it automatically converts the results to US customary, imperial, and SI metric values.
Millimeters and inches are both units used to measure length. Keep reading to learn more about each unit.
How to Convert Millimeters to Fractional Inches (1/16″, 1/32″ & 1/64″)
Plain-language method for turning decimal inches into a standard tape-measure or machinist ruler fraction
Calculators give you a decimal number (such as 0.590551 in), but tape measures and woodworking rulers are marked in binary fractions of an inch—most commonly 1/16″ on carpenter tapes, 1/32″ on fine woodworking rules, and 1/64″ on machinist scales.
Here is the step-by-step worked example for converting 15 millimeters (mm) into fractional inches:
- Find the decimal inches result: Convert 15 mm to inches to get 0.590551 in.
- Separate the whole inches from the decimal part: Keep the whole number 0 aside, leaving the decimal remainder 0.590551.
- Multiply the decimal part by your desired fraction denominator (16, 32, or 64) and round half up: Multiply 0.590551 by 16, 32, or 64, then round to the nearest whole number (values ending in .5 round up).
- Reduce the fraction to lowest terms: If the rounded top number (numerator) is even, divide both top and bottom by 2 (or their Greatest Common Divisor) until the top number is odd, then combine with your whole inches.
What Is a Millimeter?
A millimeter is a metric unit of length equal to one-thousandth (1/1,000) of a meter or one-tenth (1/10) of a centimeter. By international definition, there are exactly 25.4 millimeters in one inch. [1]
The millimeter, or millimetre, is a standard SI metric unit of length. Millimeters can be abbreviated as mm; for example, 1 millimeter can be written as 1 mm.
In the metric system, "milli" is the prefix for thousandths, or 10⁻³. Millimeters are the default unit on mechanical engineering drawings and architectural blueprints worldwide.
Millimeters are commonly measured using metric steel rules, digital vernier calipers, depth gauges, and micrometers in CNC machining, 3D printing, automotive fasteners, and precision manufacturing.
What Is an Inch?
An inch is a unit of length equal to 1/12 of a foot or 1/36 of a yard. Because the international yard is legally defined as exactly 0.9144 meters under the 1959 International Yard and Pound Agreement, one inch equals exactly 2.54 centimeters (25.4 millimeters or 25,400,000 nanometers). [2]
The inch is a US customary and imperial unit of length. Inches can be abbreviated as in; for example, 1 inch can be written as 1 in.
Inches can also be denoted using the ″ symbol, otherwise known as a double prime. Often a double quote (") is used instead of a double prime for convenience. A double prime is commonly used to express 1 in as 1″.
The standard ruler is 12 inches long and is a common tool for measuring a length in inches. Another frequently used tool to perform measurements in inches is a tape measure, which commonly comes in lengths from 6' to 35'. Other devices used to measure in inches include scales, calipers, measuring wheels, micrometers, yardsticks, and even lasers.
When converting length between millimeters (mm) and inches (in), keep full floating-point precision (1 mm = 0.0393701 in; 1 in = 25.4 mm) during intermediate calculations and round only the final inch figure to match your instrument tolerance.
More Millimeter & Inch Conversions
Need to calculate in the opposite direction? Use our inches to millimeters converter (in to mm) to switch your starting unit immediately. You can also explore related tools such as converting centimeters to inches, converting feet to inches, or converting millimeters to meters.
Convert from Millimeters
Frequently Asked Questions
References
- [1]NIST OWM StandardNIST OWM (SI Units — Length)·Length Metrology Standard — Millimeters (mm) to Inches (in)
- [2]BIPM SpecificationBIPM (SI Base Unit: Metre (m))·Unit Specifications: Millimeter (mm) & Inch (in)
- [3]NIST HB 133 ReferenceNIST HB 133 (NIST Handbook 133 (2019 Ed.))·Conversion Factors & Mathematical Basis (mm to in)