Inches to Millimeters Conversion Calculator

Enter the length in inches below to get the value converted to millimeters.

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1 in = 25.4 mm
1 in = 2.54 cm

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How to Convert Inches to Millimeters

The fastest and easiest way to convert inches (in) to millimeters (mm) is to use this simple formula:

millimeters = inches × 25.4

Since there are 25.4 millimeters in one inch, we can calculate the length in millimeters by multiplying the number of inches by 25.4.[1] Thus, the formula to convert inches to millimeters is to multiply the number of inches by 25.4.

For example, here's how to convert 5 inches to millimeters using the formula above.
millimeters = (5" × 25.4) = 127 mm
conversion scale showing inches and equivalent millimeters length values

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.

1" = 25.4 mm

Our inch fraction calculator can add inches and millimeters together, and it also 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 of measure.

infographic showing how to convert inches to millimeters

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 to be equal to exactly 0.9144 meters, one inch is equal to 2.54 centimeters.[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″.

A quarter is .955" in diameter, which is just smaller than 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' - 35'. Other types of devices used to make measurements in inches include scales, calipers, measuring wheels, micrometers, yardsticks, and even lasers.

Learn more about inches.

What Is a Millimeter?

One millimeter is equal to one-thousandth (1/1,000) of a meter, which is defined as the distance light travels in a vacuum in 1/299,792,458 of a second. One millimeter is equal to 0.0393701 inches.

The millimeter, or millimetre, is a multiple of the meter, which is the SI base unit for length. In the metric system, "milli" is the prefix for thousandths, or 10-3. Millimeters can be abbreviated as mm; for example, 1 millimeter can be written as 1 mm.

Millimeters are often represented by the smallest ticks on most metric rulers. To get a reference point of the size, the thickness of a US dime is 1.35mm.[3]

Learn more about millimeters.

We recommend using a ruler or tape measure for measuring length, which can be found at a local retailer or home center. Rulers are available in imperial, metric, or a combination of both values, so make sure you get the correct type for your needs.

Need a ruler? Try our free downloadable and printable rulers, which include both imperial and metric measurements.

Inch to Millimeter Conversion Table

Table showing various inch measurements converted to millimeters.
Inches Millimeters
1" 25.4 mm
2" 50.8 mm
3" 76.2 mm
4" 101.6 mm
5" 127 mm
6" 152.4 mm
7" 177.8 mm
8" 203.2 mm
9" 228.6 mm
10" 254 mm
11" 279.4 mm
12" 304.8 mm
13" 330.2 mm
14" 355.6 mm
15" 381 mm
16" 406.4 mm
17" 431.8 mm
18" 457.2 mm
19" 482.6 mm
20" 508 mm
21" 533.4 mm
22" 558.8 mm
23" 584.2 mm
24" 609.6 mm
25" 635 mm
26" 660.4 mm
27" 685.8 mm
28" 711.2 mm
29" 736.6 mm
30" 762 mm
31" 787.4 mm
32" 812.8 mm
33" 838.2 mm
34" 863.6 mm
35" 889 mm
36" 914.4 mm
37" 939.8 mm
38" 965.2 mm
39" 990.6 mm
40" 1,016 mm

References

  1. National Institute of Standards and Technology, SI Units - Length, https://www.nist.gov/pml/owm/si-units-length
  2. National Institute of Standards and Technology, Checking the Net Contents of Packaged Goods, Handbook 133 - 2019 Edition, https://nvlpubs.nist.gov/nistpubs/hb/2019/NIST.HB.133-2019.pdf
  3. United States Mint, Coin Specifications, https://www.usmint.gov/learn/coin-and-medal-programs/coin-specifications

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