Inch Fraction to Decimal Chart
Every sixty-fourth of an inch as a decimal and in millimeters. This is the conversion a tape measure asks for constantly and that no one memorises past sixteenths — the lines below match the marks on the tape, longest to shortest.
Source data and formula checked · How we check
Inch Fraction to Decimal Chart reads as a decimal straight off value, for 63 values from 1/64 to 63/64. Every row is computed from the same formula the calculator uses, not measured or copied from another table, so a value between two rows can be worked out the same way. The formula is the one published by NIST Office of Weights and Measures.
On a standard tape the longest mark between whole inches is 1/2, then 1/4, then 1/8, then 1/16. A tape that also marks 1/32 is usually a machinist rule rather than a builder tape.
| Value | As a decimal | As millimeters, treating it as inches |
|---|---|---|
| 1/64 | 0.01563 | 0.4 mm |
| 1/32 | 0.03125 | 0.79 mm |
| 3/64 | 0.04688 | 1.19 mm |
| 1/16 | 0.06250 | 1.59 mm |
| 5/64 | 0.07813 | 1.98 mm |
| 3/32 | 0.09375 | 2.38 mm |
| 7/64 | 0.10938 | 2.78 mm |
| 1/8 | 0.12500 | 3.18 mm |
| 9/64 | 0.14063 | 3.57 mm |
| 5/32 | 0.15625 | 3.97 mm |
| 11/64 | 0.17188 | 4.37 mm |
| 3/16 | 0.18750 | 4.76 mm |
| 13/64 | 0.20313 | 5.16 mm |
| 7/32 | 0.21875 | 5.56 mm |
| 15/64 | 0.23438 | 5.95 mm |
| 1/4 | 0.25000 | 6.35 mm |
| 17/64 | 0.26563 | 6.75 mm |
| 9/32 | 0.28125 | 7.14 mm |
| 19/64 | 0.29688 | 7.54 mm |
| 5/16 | 0.31250 | 7.94 mm |
| 21/64 | 0.32813 | 8.33 mm |
| 11/32 | 0.34375 | 8.73 mm |
| 23/64 | 0.35938 | 9.13 mm |
| 3/8 | 0.37500 | 9.52 mm |
| 25/64 | 0.39063 | 9.92 mm |
| 13/32 | 0.40625 | 10.32 mm |
| 27/64 | 0.42188 | 10.72 mm |
| 7/16 | 0.43750 | 11.11 mm |
| 29/64 | 0.45313 | 11.51 mm |
| 15/32 | 0.46875 | 11.91 mm |
| 31/64 | 0.48438 | 12.3 mm |
| 1/2 | 0.50000 | 12.7 mm |
| 33/64 | 0.51563 | 13.1 mm |
| 17/32 | 0.53125 | 13.49 mm |
| 35/64 | 0.54688 | 13.89 mm |
| 9/16 | 0.56250 | 14.29 mm |
| 37/64 | 0.57813 | 14.68 mm |
| 19/32 | 0.59375 | 15.08 mm |
| 39/64 | 0.60938 | 15.48 mm |
| 5/8 | 0.62500 | 15.88 mm |
| 41/64 | 0.64063 | 16.27 mm |
| 21/32 | 0.65625 | 16.67 mm |
| 43/64 | 0.67188 | 17.07 mm |
| 11/16 | 0.68750 | 17.46 mm |
| 45/64 | 0.70313 | 17.86 mm |
| 23/32 | 0.71875 | 18.26 mm |
| 47/64 | 0.73438 | 18.65 mm |
| 3/4 | 0.75000 | 19.05 mm |
| 49/64 | 0.76563 | 19.45 mm |
| 25/32 | 0.78125 | 19.84 mm |
| 51/64 | 0.79688 | 20.24 mm |
| 13/16 | 0.81250 | 20.64 mm |
| 53/64 | 0.82813 | 21.03 mm |
| 27/32 | 0.84375 | 21.43 mm |
| 55/64 | 0.85938 | 21.83 mm |
| 7/8 | 0.87500 | 22.22 mm |
| 57/64 | 0.89063 | 22.62 mm |
| 29/32 | 0.90625 | 23.02 mm |
| 59/64 | 0.92188 | 23.42 mm |
| 15/16 | 0.93750 | 23.81 mm |
| 61/64 | 0.95313 | 24.21 mm |
| 31/32 | 0.96875 | 24.61 mm |
| 63/64 | 0.98438 | 25 mm |
Questions people actually ask
- How do I read the Inch Fraction to Decimal Chart?
- Find your value in the first column and read across. At 1/64 as a decimal is 0.01563; at 63/64 it is 0.98438. The table runs from 1/64 to 63/64 in 63 rows.
- What if my value is outside the table?
- The chart covers 1/64 to 63/64, which is the range people actually look up. Anything above or below goes into the calculator, which takes any figure and shows each step of the working rather than only the result. Open the fraction to decimal calculator.
- Where do these numbers come from?
- Every row is computed at build time from the formula published by NIST Office of Weights and Measures, by the same code behind the calculator — not transcribed from another table, which is how a rounding error in one chart ends up in twenty.
Need a different number?
The chart covers the common values. For anything between the rows, the fraction to decimal calculator takes any figure and shows the working.
Source: NIST Office of Weights and Measures, ASME Y14.5 dimensioning and tolerancing