Decimal to Fraction Inches Calculator
Convert decimal inches or millimeters to the nearest 1/16, 1/32 or 1/64 inch, with the rounding error, plus a full chart of 64ths.
0.3125 in
| Precision | Fraction | Error (in) | Error (mm) |
|---|---|---|---|
| Nearest 1/16 | 5/16″ | +0.0000 in | +0.000 mm |
| Nearest 1/32 | 5/16″ | +0.0000 in | +0.000 mm |
| Nearest 1/64 | 5/16″ | +0.0000 in | +0.000 mm |
How it works
- Millimeters are divided by 25.4, because one inch is exactly 25.4 mm.
- The inch value is multiplied by 16, 32 and 64 and rounded to the nearest whole number of marks.
- Each fraction is reduced to lowest terms, so 8/16 shows as 1/2, and whole inches are written as a mixed number such as 2 3/8″.
Inch fractions chart: 1/64 to 1 inch
Every 64th of an inch with its exact decimal and millimeter value. All values are computed, not rounded: a 64th of an inch is exactly 0.015625 in, or 0.396875 mm.
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 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 |
Reading a tape measure
On a typical imperial tape the longest line between two inch marks is 1/2″, then 1/4″, 1/8″ and the shortest 1/16″. Counting the short marks from the last inch gives the numerator over 16. Finer rules add 1/32″ and 1/64″ marks. For general decimal-to-fraction work, use the decimal to fraction calculator.
Frequently asked questions
How do I convert a decimal to a fraction of an inch?
Multiply the decimal by the denominator you want (16, 32 or 64), round to the nearest whole number and put it over that denominator, then simplify. For 0.3125 in: 0.3125 × 16 = 5, so it is 5/16″.
What is 0.375 as a fraction of an inch?
0.375 × 8 = 3, so 0.375″ is exactly 3/8″.
How many millimeters are in an inch?
Exactly 25.4 mm. The international inch has been defined as 25.4 mm since 1959, so every millimeter value in the chart is exact.
Should I round to 1/16, 1/32 or 1/64?
Use the finest marks you can read on your tape measure or ruler. Most tape measures show 1/16″; machinists and woodworkers with fine rules often use 1/32″ or 1/64″. The calculator shows all three and how far each is from your value.
How do I convert millimeters to inch fractions?
Choose mm in the calculator. It divides by 25.4 and rounds to the nearest 1/16, 1/32 and 1/64 of an inch.
Why is my result slightly different from the decimal?
Most decimals are not an exact number of 64ths, so the fraction is rounded. The error column shows the difference in inches and millimeters.