Convert Inches to Millimeters

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

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1 in = 25.4 mm

How to Convert Inches to Millimeters

conversion scale showing inches and equivalent millimeters length values

To convert a inch measurement to a millimeter measurement, multiply the length by the conversion ratio. One inch is equal to 25.4 millimeters, so use this simple formula to convert:

millimeters = inches × 25.4

The length in millimeters is equal to the inches multiplied by 25.4.

For example, here's how to convert 5 inches to millimeters using the formula above.
5" = (5 × 25.4) = 127 mm
infographic showing how to convert inches to millimeters

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.

Inches

An inch is a unit of linear length measure 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.

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 know as a double-prime. Often a double-quote (") is used instead of a double-prime for convenience. Using the double-prime, 1 in can be written as 1″.

A quarter is .955" in diameter, which is just smaller than 1"

The standard ruler has 12", and are a common measuring tool for measuring inches. They are also often measured using tape measures which commonly come in lengths from 6' - 35'. Other types of measuring devices include scales, calipers, measuring wheels, micrometers, yardsticks, and even lasers.

Millimeters

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 a 1/299,792,458 second time interval.

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 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.

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 combination with both values, so make sure you get the correct type for your needs.

If you need a ruler you can also download and print our free printable rulers, which include both imperial and metric measurements.

Inch Measurements and Equivalent Millimeter Conversions

Common inch values converted to the equivalent millimeter value
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

More Inch Length Conversions

US Customary & Imperial Units
Convert to Miles
1" is equal to 1.5783E-5 miles
Convert to Yards
1" is equal to 0.027778 yards
Convert to Feet
1" is equal to 0.083333 feet
SI Units
Convert to Kilometers
1" is equal to 2.54E-5 kilometers
Convert to Meters
1" is equal to 0.0254 meters
Convert to Centimeters
1" is equal to 2.54 centimeters
Convert to Micrometers
1" is equal to 25,400 micrometers
Convert to Nanometers
1" is equal to 25,400,000 nanometers