Convert millimetres to inches as a fraction (to the nearest 1/16, 1/32 or 1/64 inch) and fractional or decimal inches back to millimetres. Charts for every 1/64 inch up to 1 inch, and for 1 to 50 mm, follow the converter. 1 inch = 25.4 mm exactly.
Fraction to mm chart (1/64 in to 1 in)
Values are exact: each fraction is multiplied by 25.4.
| Fraction (in) | Decimal (in) | Millimetres (mm) |
|---|---|---|
| 1/64″ | 0.015625 | 0.396875 |
| 1/32″ | 0.03125 | 0.79375 |
| 3/64″ | 0.046875 | 1.190625 |
| 1/16″ | 0.0625 | 1.5875 |
| 5/64″ | 0.078125 | 1.984375 |
| 3/32″ | 0.09375 | 2.38125 |
| 7/64″ | 0.109375 | 2.778125 |
| 1/8″ | 0.125 | 3.175 |
| 9/64″ | 0.140625 | 3.571875 |
| 5/32″ | 0.15625 | 3.96875 |
| 11/64″ | 0.171875 | 4.365625 |
| 3/16″ | 0.1875 | 4.7625 |
| 13/64″ | 0.203125 | 5.159375 |
| 7/32″ | 0.21875 | 5.55625 |
| 15/64″ | 0.234375 | 5.953125 |
| 1/4″ | 0.25 | 6.35 |
| 17/64″ | 0.265625 | 6.746875 |
| 9/32″ | 0.28125 | 7.14375 |
| 19/64″ | 0.296875 | 7.540625 |
| 5/16″ | 0.3125 | 7.9375 |
| 21/64″ | 0.328125 | 8.334375 |
| 11/32″ | 0.34375 | 8.73125 |
| 23/64″ | 0.359375 | 9.128125 |
| 3/8″ | 0.375 | 9.525 |
| 25/64″ | 0.390625 | 9.921875 |
| 13/32″ | 0.40625 | 10.31875 |
| 27/64″ | 0.421875 | 10.715625 |
| 7/16″ | 0.4375 | 11.1125 |
| 29/64″ | 0.453125 | 11.509375 |
| 15/32″ | 0.46875 | 11.90625 |
| 31/64″ | 0.484375 | 12.303125 |
| 1/2″ | 0.5 | 12.7 |
| 33/64″ | 0.515625 | 13.096875 |
| 17/32″ | 0.53125 | 13.49375 |
| 35/64″ | 0.546875 | 13.890625 |
| 9/16″ | 0.5625 | 14.2875 |
| 37/64″ | 0.578125 | 14.684375 |
| 19/32″ | 0.59375 | 15.08125 |
| 39/64″ | 0.609375 | 15.478125 |
| 5/8″ | 0.625 | 15.875 |
| 41/64″ | 0.640625 | 16.271875 |
| 21/32″ | 0.65625 | 16.66875 |
| 43/64″ | 0.671875 | 17.065625 |
| 11/16″ | 0.6875 | 17.4625 |
| 45/64″ | 0.703125 | 17.859375 |
| 23/32″ | 0.71875 | 18.25625 |
| 47/64″ | 0.734375 | 18.653125 |
| 3/4″ | 0.75 | 19.05 |
| 49/64″ | 0.765625 | 19.446875 |
| 25/32″ | 0.78125 | 19.84375 |
| 51/64″ | 0.796875 | 20.240625 |
| 13/16″ | 0.8125 | 20.6375 |
| 53/64″ | 0.828125 | 21.034375 |
| 27/32″ | 0.84375 | 21.43125 |
| 55/64″ | 0.859375 | 21.828125 |
| 7/8″ | 0.875 | 22.225 |
| 57/64″ | 0.890625 | 22.621875 |
| 29/32″ | 0.90625 | 23.01875 |
| 59/64″ | 0.921875 | 23.415625 |
| 15/16″ | 0.9375 | 23.8125 |
| 61/64″ | 0.953125 | 24.209375 |
| 31/32″ | 0.96875 | 24.60625 |
| 63/64″ | 0.984375 | 25.003125 |
| 1″ | 1 | 25.4 |
mm to inches chart (1 to 50 mm)
Decimal inches rounded to 4 places; the difference column shows how far the nearest 1/64 inch fraction is from the true millimetre value.
| Millimetres (mm) | Decimal (in) | Nearest 1/64 in | Difference (mm) |
|---|---|---|---|
| 1 | 0.0394 | 3/64″ | +0.191 |
| 2 | 0.0787 | 5/64″ | -0.016 |
| 3 | 0.1181 | 1/8″ | +0.175 |
| 4 | 0.1575 | 5/32″ | -0.031 |
| 5 | 0.1969 | 13/64″ | +0.159 |
| 6 | 0.2362 | 15/64″ | -0.047 |
| 7 | 0.2756 | 9/32″ | +0.144 |
| 8 | 0.3150 | 5/16″ | -0.062 |
| 9 | 0.3543 | 23/64″ | +0.128 |
| 10 | 0.3937 | 25/64″ | -0.078 |
| 11 | 0.4331 | 7/16″ | +0.112 |
| 12 | 0.4724 | 15/32″ | -0.094 |
| 13 | 0.5118 | 33/64″ | +0.097 |
| 14 | 0.5512 | 35/64″ | -0.109 |
| 15 | 0.5906 | 19/32″ | +0.081 |
| 16 | 0.6299 | 5/8″ | -0.125 |
| 17 | 0.6693 | 43/64″ | +0.066 |
| 18 | 0.7087 | 45/64″ | -0.141 |
| 19 | 0.7480 | 3/4″ | +0.050 |
| 20 | 0.7874 | 25/32″ | -0.156 |
| 21 | 0.8268 | 53/64″ | +0.034 |
| 22 | 0.8661 | 55/64″ | -0.172 |
| 23 | 0.9055 | 29/32″ | +0.019 |
| 24 | 0.9449 | 15/16″ | -0.188 |
| 25 | 0.9843 | 63/64″ | +0.003 |
| 26 | 1.0236 | 1 1/32″ | +0.194 |
| 27 | 1.0630 | 1 1/16″ | -0.012 |
| 28 | 1.1024 | 1 7/64″ | +0.178 |
| 29 | 1.1417 | 1 9/64″ | -0.028 |
| 30 | 1.1811 | 1 3/16″ | +0.162 |
| 31 | 1.2205 | 1 7/32″ | -0.044 |
| 32 | 1.2598 | 1 17/64″ | +0.147 |
| 33 | 1.2992 | 1 19/64″ | -0.059 |
| 34 | 1.3386 | 1 11/32″ | +0.131 |
| 35 | 1.3780 | 1 3/8″ | -0.075 |
| 36 | 1.4173 | 1 27/64″ | +0.116 |
| 37 | 1.4567 | 1 29/64″ | -0.091 |
| 38 | 1.4961 | 1 1/2″ | +0.100 |
| 39 | 1.5354 | 1 17/32″ | -0.106 |
| 40 | 1.5748 | 1 37/64″ | +0.084 |
| 41 | 1.6142 | 1 39/64″ | -0.122 |
| 42 | 1.6535 | 1 21/32″ | +0.069 |
| 43 | 1.6929 | 1 11/16″ | -0.138 |
| 44 | 1.7323 | 1 47/64″ | +0.053 |
| 45 | 1.7717 | 1 49/64″ | -0.153 |
| 46 | 1.8110 | 1 13/16″ | +0.038 |
| 47 | 1.8504 | 1 27/32″ | -0.169 |
| 48 | 1.8898 | 1 57/64″ | +0.022 |
| 49 | 1.9291 | 1 59/64″ | -0.184 |
| 50 | 1.9685 | 1 31/32″ | +0.006 |
How to convert
- Inches to mm: multiply by 25.4. 3/8 in = 0.375 × 25.4 = 9.525 mm.
- mm to inches: divide by 25.4. 10 mm = 0.3937 in.
- mm to a fraction: divide by 25.4, multiply by 64, round to a whole number and reduce. 10 mm → 0.3937 × 64 = 25.2 → 25/64 in.
Fractional and metric tube sizes are not interchangeable
Instrument and hydraulic tube is sold in both fractional-inch and metric outside diameters, and the nearest sizes are close but not equal: 1/4 in is 6.35 mm, not 6 mm; 1/2 in is 12.7 mm, not 12 mm. Fittings and ferrules must match the tube OD system, so order tube by the exact OD in the system your fittings use. See the hydraulic tubing guide and the pipe schedule chart for pipe sizes, and other tools in the technical resources index.
Frequently asked questions
How do you convert mm to inches as a fraction?
Divide millimetres by 25.4 to get decimal inches, multiply by 64 (or 32, or 16), round to a whole number and reduce the fraction. For example, 10 mm is 0.3937 in, about 25/64 in.
How many mm is 1/4 inch?
1/4 inch is 6.35 mm exactly (0.25 × 25.4).
How many mm is 3/8 inch?
3/8 inch is 9.525 mm.
Is 6 mm tube the same as 1/4 inch tube?
No. 1/4 inch is 6.35 mm, so 6 mm and 1/4 inch tube need different fittings.
