Inches to Millimeters Converter
Enter the length in inches below to convert it to millimeters.
Convert Inches to Millimeters
Enter a value in inches (in) to convert to millimeters (mm).
Inches to Millimeters Conversion Chart (1–40 Continuous)
Continuous 1 to 40 inches lookup table with exact decimals and reduced nearest 1/64 fractions. Highlighted rows mark common shop and ruler values.
| Inches (in) | Decimal (mm) | Fraction — Nearest 1/64 (Reduced) | Nearest 1/16 (Tape) |
|---|---|---|---|
1 in★ Common | 25.4 mm | 25 13/32 mm | 25 3/8 mm |
2 in★ Common | 50.8 mm | 50 51/64 mm | 50 13/16 mm |
3 in★ Common | 76.2 mm | 76 13/64 mm | 76 3/16 mm |
4 in | 101.6 mm | 101 19/32 mm | 101 5/8 mm |
5 in★ Common | 127 mm | 127 mm | 127 mm |
6 in★ Common | 152.4 mm | 152 13/32 mm | 152 3/8 mm |
7 in | 177.8 mm | 177 51/64 mm | 177 13/16 mm |
8 in★ Common | 203.2 mm | 203 13/64 mm | 203 3/16 mm |
9 in | 228.6 mm | 228 19/32 mm | 228 5/8 mm |
10 in★ Common | 254 mm | 254 mm | 254 mm |
11 in | 279.4 mm | 279 13/32 mm | 279 3/8 mm |
12 in★ Common | 304.8 mm | 304 51/64 mm | 304 13/16 mm |
How to Convert Inches to Millimeters
To convert inches to millimeters, multiply the length by the following conversion ratio: 25.4 millimeters/inch.
Since one inch is equal to 25.4 millimeters, you can use this simple formula to convert:
The length in millimeters is equal to the length in inches multiplied by 25.4.
For example, here's how to convert 5 inches to millimeters using the formula above.
How Many Millimeters Are in an Inch?
There are 25.4 millimeters in an inch, which is why we use this value in the formula above.
Our inch fraction and decimal calculator can convert inches and millimeters, and it automatically converts the results to US customary, imperial, and SI metric values.
Inches and millimeters are both units used to measure length. Keep reading to learn more about each unit.
How to Convert Inches 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 5 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 5 inches (in) into fractional inches:
- Find the decimal inches result: Convert 5 in to inches to get 5 in.
- Separate the whole inches from the decimal part: Keep the whole number 5 aside, leaving the decimal remainder 0.
- Multiply the decimal part by your desired fraction denominator (16, 32, or 64) and round half up: Multiply 0 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 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). [1]
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.
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. [2]
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.
When converting length between inches (in) and millimeters (mm), keep full floating-point precision (1" = 25.4 mm; 1 mm = 0.0393701 in) during intermediate calculations and round only the final millimeter figure to match your instrument tolerance.
More Inch & Millimeter Conversions
Need to calculate in the opposite direction? Use our millimeters to inches converter (mm to in) to switch your starting unit immediately. You can also explore related tools such as converting micrometers to millimeters, converting meters to millimeters, or converting inches to centimeters.
Convert from Inches
Frequently Asked Questions
References
- [1]NIST OWM StandardNIST OWM (SI Units — Length)·Length Metrology Standard — Inches (in) to Millimeters (mm)
- [2]BIPM SpecificationBIPM (SI Base Unit: Metre (m))·Unit Specifications: Inch (in) & Millimeter (mm)
- [3]NIST HB 133 ReferenceNIST HB 133 (NIST Handbook 133 (2019 Ed.))·Conversion Factors & Mathematical Basis (in to mm)