Fractional sizes follow rational inch steps, number sizes run from #80 toward #1 as diameter increases, and letter sizes run A through Z. Metric drills are labeled directly in millimeters.
Fractional drill sizes by sixty-fourths
Number and letter drills continue in the companion table below the fractional series. Values in millimeters are exact conversions rounded to three decimals.
| Fraction | Decimal inches | Millimeters |
|---|---|---|
| 1/64 in | 0.015625 | 0.397 |
| 2/64 in | 0.031250 | 0.794 |
| 3/64 in | 0.046875 | 1.191 |
| 4/64 in | 0.062500 | 1.588 |
| 5/64 in | 0.078125 | 1.984 |
| 6/64 in | 0.093750 | 2.381 |
| 7/64 in | 0.109375 | 2.778 |
| 8/64 in | 0.125000 | 3.175 |
| 9/64 in | 0.140625 | 3.572 |
| 10/64 in | 0.156250 | 3.969 |
| 11/64 in | 0.171875 | 4.366 |
| 12/64 in | 0.187500 | 4.763 |
| 13/64 in | 0.203125 | 5.159 |
| 14/64 in | 0.218750 | 5.556 |
| 15/64 in | 0.234375 | 5.953 |
| 16/64 in | 0.250000 | 6.350 |
| 17/64 in | 0.265625 | 6.747 |
| 18/64 in | 0.281250 | 7.144 |
| 19/64 in | 0.296875 | 7.541 |
| 20/64 in | 0.312500 | 7.938 |
| 21/64 in | 0.328125 | 8.334 |
| 22/64 in | 0.343750 | 8.731 |
| 23/64 in | 0.359375 | 9.128 |
| 24/64 in | 0.375000 | 9.525 |
| 25/64 in | 0.390625 | 9.922 |
| 26/64 in | 0.406250 | 10.319 |
| 27/64 in | 0.421875 | 10.716 |
| 28/64 in | 0.437500 | 11.113 |
| 29/64 in | 0.453125 | 11.509 |
| 30/64 in | 0.468750 | 11.906 |
| 31/64 in | 0.484375 | 12.303 |
| 32/64 in | 0.500000 | 12.700 |
Number and letter drill sizes
| Designation | Series | Diameter (in) | Diameter (mm) |
|---|---|---|---|
| #1 | number | .2280 | 5.791 |
| #2 | number | .2210 | 5.613 |
| #3 | number | .2130 | 5.410 |
| #4 | number | .2090 | 5.309 |
| #5 | number | .2055 | 5.220 |
| #6 | number | .2040 | 5.182 |
| #7 | number | .2010 | 5.105 |
| #8 | number | .1990 | 5.055 |
| #9 | number | .1960 | 4.978 |
| #10 | number | .1935 | 4.915 |
| #11 | number | .1910 | 4.851 |
| #12 | number | .1890 | 4.801 |
| #13 | number | .1850 | 4.699 |
| #14 | number | .1820 | 4.623 |
| #15 | number | .1800 | 4.572 |
| #16 | number | .1770 | 4.496 |
| #17 | number | .1730 | 4.394 |
| #18 | number | .1695 | 4.305 |
| #19 | number | .1660 | 4.216 |
| #20 | number | .1610 | 4.089 |
| #21 | number | .1590 | 4.039 |
| #22 | number | .1570 | 3.988 |
| #23 | number | .1540 | 3.912 |
| #24 | number | .1520 | 3.861 |
| #25 | number | .1495 | 3.797 |
| #26 | number | .1470 | 3.734 |
| #27 | number | .1440 | 3.658 |
| #28 | number | .1405 | 3.569 |
| #29 | number | .1360 | 3.454 |
| #30 | number | .1285 | 3.264 |
| #31 | number | .1200 | 3.048 |
| #32 | number | .1160 | 2.946 |
| #33 | number | .1130 | 2.870 |
| #34 | number | .1110 | 2.819 |
| #35 | number | .1100 | 2.794 |
| #36 | number | .1065 | 2.705 |
| #37 | number | .1040 | 2.642 |
| #38 | number | .1015 | 2.578 |
| #39 | number | .0995 | 2.527 |
| #40 | number | .0980 | 2.489 |
| #41 | number | .0960 | 2.438 |
| #42 | number | .0935 | 2.375 |
| #43 | number | .0890 | 2.261 |
| #44 | number | .0860 | 2.184 |
| #45 | number | .0820 | 2.083 |
| #46 | number | .0810 | 2.057 |
| #47 | number | .0785 | 1.994 |
| #48 | number | .0760 | 1.930 |
| #49 | number | .0730 | 1.854 |
| #50 | number | .0700 | 1.778 |
| #51 | number | .0670 | 1.702 |
| #52 | number | .0635 | 1.613 |
| #53 | number | .0595 | 1.511 |
| #54 | number | .0550 | 1.397 |
| #55 | number | .0520 | 1.321 |
| #56 | number | .0465 | 1.181 |
| #57 | number | .0430 | 1.092 |
| #58 | number | .0420 | 1.067 |
| #59 | number | .0410 | 1.041 |
| #60 | number | .0400 | 1.016 |
| #61 | number | .0390 | 0.991 |
| #62 | number | .0380 | 0.965 |
| #63 | number | .0370 | 0.940 |
| #64 | number | .0360 | 0.914 |
| #65 | number | .0350 | 0.889 |
| #66 | number | .0330 | 0.838 |
| #67 | number | .0320 | 0.813 |
| #68 | number | .0310 | 0.787 |
| #69 | number | .0292 | 0.742 |
| #70 | number | .0280 | 0.711 |
| #71 | number | .0260 | 0.660 |
| #72 | number | .0250 | 0.635 |
| #73 | number | .0240 | 0.610 |
| #74 | number | .0225 | 0.572 |
| #75 | number | .0210 | 0.533 |
| #76 | number | .0200 | 0.508 |
| #77 | number | .0180 | 0.457 |
| #78 | number | .0160 | 0.406 |
| #79 | number | .0145 | 0.368 |
| #80 | number | .0135 | 0.343 |
| A | letter | .2340 | 5.944 |
| B | letter | .2380 | 6.045 |
| C | letter | .2420 | 6.147 |
| D | letter | .2460 | 6.248 |
| E | letter | .2500 | 6.350 |
| F | letter | .2570 | 6.528 |
| G | letter | .2610 | 6.629 |
| H | letter | .2660 | 6.756 |
| I | letter | .2720 | 6.909 |
| J | letter | .2770 | 7.036 |
| K | letter | .2810 | 7.137 |
| L | letter | .2900 | 7.366 |
| M | letter | .2950 | 7.493 |
| N | letter | .3020 | 7.671 |
| O | letter | .3160 | 8.026 |
| P | letter | .3230 | 8.204 |
| Q | letter | .3320 | 8.433 |
| R | letter | .3390 | 8.611 |
| S | letter | .3480 | 8.839 |
| T | letter | .3580 | 9.093 |
| U | letter | .3680 | 9.347 |
| V | letter | .3770 | 9.576 |
| W | letter | .3860 | 9.804 |
| X | letter | .3970 | 10.084 |
| Y | letter | .4040 | 10.262 |
| Z | letter | .4130 | 10.490 |
Designation systems are not one scale
A #7 drill is not 7/64 inch, and an F drill is not a fractional grade. Number and letter designations must be looked up before comparison.
- Fractional: divide numerator by denominator.
- Metric: retain millimeters or divide by 25.4 for inches.
- Number/letter: use a reviewed lookup table.
Nominal versus measured holes
A drill’s designation is its nominal cutting diameter. Machine condition, runout, point geometry, material and wear can make the produced hole differ from the label.
Important limitation
A converted size is mathematically equivalent, not proof that the available drill will produce an identical finished hole in a specific process.
A converted size is mathematically equivalent, not proof that the available drill will produce an identical finished hole in a specific process.
Technical references
- Decimal Equivalent & Drill Size Chart — Travers Tool Co.. Accessed 2026-11-09.
- SI Units – Length — National Institute of Standards and Technology. Accessed 2026-11-09.
Standards references identify scope and terminology; protected dimensional tables are not reproduced.