Skip to content
UnitCheck

Browse all tools

Inches to Millimeters Converter

1 inch is exactly 25.4 millimeters. To convert inches to millimeters, multiply by 25.4.

Sources: NIST SP 811, NIST Handbook 44, BIPM SI Brochure Updated

Result

1 in = 25.4 mm

Inch fractions

How to convert inches to millimeters

millimeters = inches × 25.4

1 inch is exactly 25.4 millimeters. 1 millimeter is one thousandth of a meter (SI prefix milli, 10⁻³).

The factor 25.4 is exact, not a rounded value. Nothing is rounded until you choose how many decimals to show.

Worked example: 3.5 in

  1. Start with the value in inches: 3.5 in.
  2. Multiply by 25.4, because 1 inch = 25.4 millimeters: 3.5 × 25.4 = 88.9 mm.

Inches and millimeters side by side

inmm00.511.522.533.54020406080100
Inches on top, millimeters below, lined up with the exact factor. The line marks the value in the converter. Drawn to proportion, not to actual size.

Inches to millimeters chart

Inches from 1 to 100 converted to millimeters with the exact factor, shown to five significant digits.

Inches to millimeters, part 1 of 4
inmm
125.4
250.8
376.2
4101.6
5127
6152.4
7177.8
8203.2
9228.6
10254
11279.4
12304.8
13330.2
14355.6
15381
16406.4
17431.8
18457.2
19482.6
20508
21533.4
22558.8
23584.2
24609.6
25635
Inches to millimeters, part 2 of 4
inmm
26660.4
27685.8
28711.2
29736.6
30762
31787.4
32812.8
33838.2
34863.6
35889
36914.4
37939.8
38965.2
39990.6
401,016
411,041.4
421,066.8
431,092.2
441,117.6
451,143
461,168.4
471,193.8
481,219.2
491,244.6
501,270
Inches to millimeters, part 3 of 4
inmm
511,295.4
521,320.8
531,346.2
541,371.6
551,397
561,422.4
571,447.8
581,473.2
591,498.6
601,524
611,549.4
621,574.8
631,600.2
641,625.6
651,651
661,676.4
671,701.8
681,727.2
691,752.6
701,778
711,803.4
721,828.8
731,854.2
741,879.6
751,905
Inches to millimeters, part 4 of 4
inmm
761,930.4
771,955.8
781,981.2
792,006.6
802,032
812,057.4
822,082.8
832,108.2
842,133.6
852,159
862,184.4
872,209.8
882,235.2
892,260.6
902,286
912,311.4
922,336.8
932,362.2
942,387.6
952,413
962,438.4
972,463.8
982,489.2
992,514.6
1002,540

Fractions of an inch in decimals and millimeters

Every value is exact: 1 inch is 25.4 mm by definition.

Inch fractions in decimals and millimeters, part 1 of 2
FractionDecimal inmm
1/64 in0.0156250.396875
1/32 in0.031250.79375
3/64 in0.0468751.190625
1/16 in0.06251.5875
5/64 in0.0781251.984375
3/32 in0.093752.38125
7/64 in0.1093752.778125
1/8 in0.1253.175
9/64 in0.1406253.571875
5/32 in0.156253.96875
11/64 in0.1718754.365625
3/16 in0.18754.7625
13/64 in0.2031255.159375
7/32 in0.218755.55625
15/64 in0.2343755.953125
1/4 in0.256.35
17/64 in0.2656256.746875
9/32 in0.281257.14375
19/64 in0.2968757.540625
5/16 in0.31257.9375
21/64 in0.3281258.334375
11/32 in0.343758.73125
23/64 in0.3593759.128125
3/8 in0.3759.525
25/64 in0.3906259.921875
13/32 in0.4062510.31875
27/64 in0.42187510.715625
7/16 in0.437511.1125
29/64 in0.45312511.509375
15/32 in0.4687511.90625
31/64 in0.48437512.303125
1/2 in0.512.7
Inch fractions in decimals and millimeters, part 2 of 2
FractionDecimal inmm
33/64 in0.51562513.096875
17/32 in0.5312513.49375
35/64 in0.54687513.890625
9/16 in0.562514.2875
37/64 in0.57812514.684375
19/32 in0.5937515.08125
39/64 in0.60937515.478125
5/8 in0.62515.875
41/64 in0.64062516.271875
21/32 in0.6562516.66875
43/64 in0.67187517.065625
11/16 in0.687517.4625
45/64 in0.70312517.859375
23/32 in0.7187518.25625
47/64 in0.73437518.653125
3/4 in0.7519.05
49/64 in0.76562519.446875
25/32 in0.7812519.84375
51/64 in0.79687520.240625
13/16 in0.812520.6375
53/64 in0.82812521.034375
27/32 in0.8437521.43125
55/64 in0.85937521.828125
7/8 in0.87522.225
57/64 in0.89062522.621875
29/32 in0.9062523.01875
59/64 in0.92187523.415625
15/16 in0.937523.8125
61/64 in0.95312524.209375
31/32 in0.9687524.60625
63/64 in0.98437525.003125
1 in125.4

millimeters = inches × 25.4. Factors: NIST SP 811, NIST Handbook 44, BIPM SI Brochure. unitcheck.net/length/inches-to-millimeters/

Common values

InchesMillimetersWhat it is
1/4 in6.35 mm
1/2 in12.7 mm
1 in25.4 mm
12 in304.8 mm1 foot

Going the other way? Use the Millimeters to Inches converter.

Frequently asked questions

How many millimeters are in 1 inch?

1 inch is exactly 25.4 millimeters. 1 millimeter is one thousandth of a meter (SI prefix milli, 10⁻³).

How do I convert inches to millimeters?

Multiply by 25.4: millimeters = inches × 25.4. For example, 3.5 in = 88.9 mm.

How many inches are in 1 millimeter?

1 millimeter is about 0.0393701 inches. To go the other way, use the millimeters to inches converter.

Is the in to mm conversion exact?

Yes. 1 millimeter is one thousandth of a meter (SI prefix milli, 10⁻³). The factor 25.4 follows from the definitions, so the only rounding is in the number of decimals you display.

Can I type a fraction such as 3 5/8?

Yes. The inches field accepts decimals (3.625), fractions (5/8) and mixed numbers (3 5/8). All three are read exactly.

Sources

More in Length