Convert inches to millimeters
1 in = 25.4 mm — exactly. Both units are defined against the SI, so this factor is a fraction, not an approximation.
25.4mm
As a fraction: 127/5
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1 in = 25.4 mm
Show this value in all 50 length units
- Gigameters Gm 2.54e-11
- Megameters Mm 2.54e-8
- Kilometers km 0.000 025 4
- Hectometers hm 0.000 254
- Decameters dam 0.002 54
- Meters m 0.0254
- Decimeters dm 0.254
- Centimeters cm 2.54
- Millimeters mm 25.4
- Micrometers µm 25 400
- Nanometers nm 25 400 000
- Picometers pm 25 400 000 000
- Femtometers fm 25 400 000 000 000
- Inches in 1
- Feet ft 0.083 333 333 333 3
- Yards yd 0.027 777 777 777 8
- Miles mi 0.000 015 782 828 282 8
- Nautical miles nmi 0.000 013 714 902 807 8
- Thous thou 1000
- Hands hh 0.25
- Links li 0.126 262 626 263
- Spans span 0.111 111 111 111
- Cubits cubit 0.055 555 555 555 6
- Ells ell 0.022 222 222 222 2
- Fathoms ftm 0.013 888 888 888 9
- Rods rd 0.005 050 505 050 51
- Chains ch 0.001 262 626 262 63
- Furlongs fur 0.000 126 262 626 263
- Leagues lea 0.000 005 260 942 760 94
- Barleycorns barleycorn 3
- US survey feet ft (US) 0.083 333 166 666 7
- US survey miles mi (US) 0.000 015 782 796 717 2
- Ångströms Å 254 000 000
- Microns µ 25 400
- Bohr radiuss a₀ 479 990 435.981
- Planck lengths ℓₚ 1.57153419479e+33
- Astronomical units au 1.69788512906e-13
- Light-years ly 2.68478211842e-18
- Light-seconds ls 8.47252801803e-11
- Light-minutes lmin 1.41208800301e-12
- Parsecs pc 8.23157939519e-19
- Kiloparsecs kpc 8.23157939519e-22
- Megaparsecs Mpc 8.23157939519e-25
- Solar radiuss R☉ 3.65099899382e-11
- Earth radiuss R🜨 3.98681525663e-9
- Point (DTP)s pt 72
- Picas pc 6
- Scandinavian miles mil 0.000 002 54
- Versts вер 0.000 023 809 523 809 5
- Lis 里 0.000 050 8
Every row is Inch (in) converted through the meter, in exact rational arithmetic.
How to convert inches to millimeters
Multiply the number of inches by 25.4 to get millimeters.
The exact factor is 25.4 — as a fraction, 127/5.
Inch: Defined as exactly 25.4 mm by the 1959 international yard and pound agreement.
Inch to Millimeter conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 in | 25.4 |
| 2 in | 50.8 |
| 3 in | 76.2 |
| 5 in | 127 |
| 10 in | 254 |
| 20 in | 508 |
| 25 in | 635 |
| 50 in | 1270 |
| 100 in | 2540 |
| 250 in | 6350 |
| 500 in | 12 700 |
| 1000 in | 25 400 |
Millimeter to Inch conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.039 370 079 |
| 2 mm | 0.078 740 157 |
| 3 mm | 0.118 110 24 |
| 5 mm | 0.196 850 39 |
| 10 mm | 0.393 700 79 |
| 20 mm | 0.787 401 57 |
| 25 mm | 0.984 251 97 |
| 50 mm | 1.968 503 9 |
| 100 mm | 3.937 007 9 |
| 250 mm | 9.842 519 7 |
| 500 mm | 19.685 039 |
| 1000 mm | 39.370 079 |
Frequently asked
How many millimeters are in a inch?
One inch equals 25.4 millimeters (in → mm). That figure is exact, not rounded.
How do you convert inches to millimeters?
Multiply the number of inches by 25.4 to get millimeters.
What is 1 mm in inches?
One millimeter is 0.03937007874 inches.
What is 10 in in mm?
10 in = 254 mm.
What exactly is a inch?
Defined as exactly 25.4 mm by the 1959 international yard and pound agreement.