How to Convert Millimeters to Inches

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

Since there are 25.4 millimeters in one inch<1>, the length in inches is equal to millimeters divided by 25.4.Thus, the formula to convert millimeters to inches is the length divided by 25.4.

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How to Convert mm to Fractional Inches

You"ve learned how to convert millimeters to inches, but you might be wondering how to convert mm to fractional inches.

Start with the mm to inches conversion above to get the result in decimal form first, then round to the nearest fractional inch.

Take the portion of the decimal result to the right of the decimal point and multiply it by the level of precision you want.You can choose to round to the nearest 1/16, 1/32, or 1/64 of an inch.

To round to the nearest 1/16, for example, take the decimal portion and multiply it by 16.Then, round that result to get the numerator of the fractional inch measurement.

For example, convert 100 mm to fractional inches to 1/16" precision following these steps.

Divide 100 by 25.4 to convert mm to inches.

100 mm ÷ 25.4 = 3.937 in

Then, multiply the decimal remainder by 16.

0.937 × 16 = 14.992

Round this to the nearest whole number; in this case, 14.992 can be rounded to 15.Place this value in a fraction over 16, so 15/16 is the remaining fraction.

Put it all together by placing the whole number in the decimal in front of the fraction.

100 mm ≈ 3 15/16"

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


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 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.<2>

What is an Inch?

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.<3>

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 has 12", and is 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.

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.

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

mm to Inches Conversion Chart

Chart of millimeter measurements converted to inches and fractional inches rounded to the nearest 1/64"MillimetersInches (decimal)Inches (fraction)
1 mm0.03937"3/64"
2 mm0.07874"5/64"
3 mm0.11811"1/8"
4 mm0.15748"5/32"
5 mm0.19685"13/64"
6 mm0.23622"15/64"
7 mm0.275591"9/32"
8 mm0.314961"5/16"
9 mm0.354331"23/64"
10 mm0.393701"25/64"
11 mm0.433071"7/16"
12 mm0.472441"15/32"
13 mm0.511811"33/64"
14 mm0.551181"35/64"
15 mm0.590551"19/32"
16 mm0.629921"5/8"
17 mm0.669291"43/64"
18 mm0.708661"45/64"
19 mm0.748031"3/4"
20 mm0.787402"25/32"
21 mm0.826772"53/64"
22 mm0.866142"55/64"
23 mm0.905512"29/32"
24 mm0.944882"15/16"
25 mm0.984252"63/64"
26 mm1.0236"1 1/32"
27 mm1.063"1 1/16"
28 mm1.1024"1 7/64"
29 mm1.1417"1 9/64"
30 mm1.1811"1 3/16"
31 mm1.2205"1 7/32"
32 mm1.2598"1 17/64"
33 mm1.2992"1 19/64"
34 mm1.3386"1 11/32"
35 mm1.378"1 3/8"
36 mm1.4173"1 27/64"
37 mm1.4567"1 29/64"
38 mm1.4961"1 1/2"
39 mm1.5354"1 17/32"
40 mm1.5748"1 37/64"


National Institute of Standards and Technology, SI Units - Length, States Mint, Coin Specifications, Institute of Standards and Technology, Checking the Net Contents of Packaged Goods, Handbook 133 - 2019 Edition,