Complete drill bit size conversion chart with fractional, metric (mm), and letter drill bit sizes. Essential reference for precision drilling and CNC machining operations.
Drill bits are sized using three main systems: fractional (inches), number sizes, and letter sizes. This comprehensive chart provides conversions between all three systems plus metric equivalents, making it easy to find the right drill bit for any application.
Number drill bits range from #80 (smallest) to #1 (largest), while letter drill bits range from A (smallest) to Z (largest). Understanding these sizing systems is crucial for precision drilling in CNC machining and manufacturing.
| Size | Decimal (inch) | Metric (mm) | Type |
|---|---|---|---|
| #80 | 0.0135 | 0.343 | Number |
| #79 | 0.0145 | 0.368 | Number |
| 1/64" | 0.0156 | 0.397 | Fractional |
| #78 | 0.0160 | 0.406 | Number |
| #77 | 0.0180 | 0.457 | Number |
| #76 | 0.0200 | 0.508 | Number |
| #75 | 0.0210 | 0.533 | Number |
| #74 | 0.0225 | 0.572 | Number |
| #73 | 0.0240 | 0.610 | Number |
| #72 | 0.0250 | 0.635 | Number |
| #71 | 0.0260 | 0.660 | Number |
| #70 | 0.0280 | 0.711 | Number |
| #69 | 0.0292 | 0.742 | Number |
| #68 | 0.0310 | 0.787 | Number |
| 1/32" | 0.0312 | 0.794 | Fractional |
| #67 | 0.0320 | 0.813 | Number |
| #66 | 0.0330 | 0.838 | Number |
| #65 | 0.0350 | 0.889 | Number |
| #64 | 0.0360 | 0.914 | Number |
| #63 | 0.0370 | 0.940 | Number |
| #62 | 0.0380 | 0.965 | Number |
| #61 | 0.0390 | 0.991 | Number |
| #60 | 0.0400 | 1.016 | Number |
| #59 | 0.0410 | 1.041 | Number |
| #58 | 0.0420 | 1.067 | Number |
| #57 | 0.0430 | 1.092 | Number |
| #56 | 0.0465 | 1.181 | Number |
| 3/64" | 0.0469 | 1.191 | Fractional |
| #55 | 0.0520 | 1.321 | Number |
| #54 | 0.0550 | 1.397 | Number |
| #53 | 0.0595 | 1.511 | Number |
| 1/16" | 0.0625 | 1.588 | Fractional |
| #52 | 0.0635 | 1.613 | Number |
| #51 | 0.0670 | 1.702 | Number |
| #50 | 0.0700 | 1.778 | Number |
| #49 | 0.0730 | 1.854 | Number |
| #48 | 0.0760 | 1.930 | Number |
| 5/64" | 0.0781 | 1.984 | Fractional |
| #47 | 0.0785 | 1.994 | Number |
| #46 | 0.0810 | 2.057 | Number |
| #45 | 0.0820 | 2.083 | Number |
| #44 | 0.0860 | 2.184 | Number |
| #43 | 0.0890 | 2.261 | Number |
| #42 | 0.0935 | 2.375 | Number |
| 3/32" | 0.0938 | 2.381 | Fractional |
| #41 | 0.0960 | 2.438 | Number |
| #40 | 0.0980 | 2.489 | Number |
| #39 | 0.0995 | 2.527 | Number |
| #38 | 0.1015 | 2.578 | Number |
| #37 | 0.1040 | 2.642 | Number |
| #36 | 0.1065 | 2.705 | Number |
| 7/64" | 0.1094 | 2.778 | Fractional |
| #35 | 0.1100 | 2.794 | Number |
| #34 | 0.1110 | 2.819 | Number |
| #33 | 0.1130 | 2.870 | Number |
| #32 | 0.1160 | 2.946 | Number |
| #31 | 0.1200 | 3.048 | Number |
| 1/8" | 0.1250 | 3.175 | Fractional |
| #30 | 0.1285 | 3.264 | Number |
| #29 | 0.1360 | 3.454 | Number |
| #28 | 0.1405 | 3.569 | Number |
| 9/64" | 0.1406 | 3.571 | Fractional |
| #27 | 0.1440 | 3.658 | Number |
| #26 | 0.1470 | 3.734 | Number |
| #25 | 0.1495 | 3.797 | Number |
| #24 | 0.1520 | 3.861 | Number |
| #23 | 0.1540 | 3.912 | Number |
| 5/32" | 0.1562 | 3.969 | Fractional |
| #22 | 0.1570 | 3.988 | Number |
| #21 | 0.1590 | 4.039 | Number |
| #20 | 0.1610 | 4.089 | Number |
| #19 | 0.1660 | 4.216 | Number |
| #18 | 0.1695 | 4.305 | Number |
| 11/64" | 0.1719 | 4.366 | Fractional |
| #17 | 0.1730 | 4.394 | Number |
| #16 | 0.1770 | 4.496 | Number |
| #15 | 0.1800 | 4.572 | Number |
| #14 | 0.1820 | 4.623 | Number |
| #13 | 0.1850 | 4.699 | Number |
| 3/16" | 0.1875 | 4.762 | Fractional |
| #12 | 0.1890 | 4.801 | Number |
| #11 | 0.1910 | 4.851 | Number |
| #10 | 0.1935 | 4.915 | Number |
| #9 | 0.1960 | 4.978 | Number |
| #8 | 0.1990 | 5.055 | Number |
| #7 | 0.2010 | 5.105 | Number |
| 13/64" | 0.2031 | 5.159 | Fractional |
| #6 | 0.2040 | 5.182 | Number |
| #5 | 0.2055 | 5.220 | Number |
| #4 | 0.2090 | 5.309 | Number |
| #3 | 0.2130 | 5.410 | Number |
| 7/32" | 0.2188 | 5.556 | Fractional |
| #2 | 0.2210 | 5.613 | Number |
| #1 | 0.2280 | 5.791 | Number |
| A | 0.2340 | 5.944 | Letter |
| 15/64" | 0.2344 | 5.953 | Fractional |
| 1/4" | 0.2500 | 6.350 | Fractional |
| B | 0.2380 | 6.045 | Letter |
| C | 0.2420 | 6.147 | Letter |
| D | 0.2460 | 6.248 | Letter |
| E | 0.2500 | 6.350 | Letter |
| F | 0.2570 | 6.528 | Letter |
| 17/64" | 0.2656 | 6.747 | Fractional |
| G | 0.2610 | 6.629 | Letter |
| H | 0.2660 | 6.756 | Letter |
| I | 0.2720 | 6.909 | Letter |
| J | 0.2770 | 7.036 | Letter |
| 9/32" | 0.2812 | 7.144 | Fractional |
| K | 0.2810 | 7.137 | Letter |
| L | 0.2900 | 7.366 | Letter |
| M | 0.2950 | 7.493 | Letter |
| 19/64" | 0.2969 | 7.541 | Fractional |
| N | 0.3020 | 7.671 | Letter |
| 5/16" | 0.3125 | 7.938 | Fractional |
| O | 0.3160 | 8.026 | Letter |
| P | 0.3230 | 8.204 | Letter |
| 21/64" | 0.3281 | 8.334 | Fractional |
| Q | 0.3320 | 8.433 | Letter |
| R | 0.3390 | 8.611 | Letter |
| 11/32" | 0.3438 | 8.731 | Fractional |
| S | 0.3480 | 8.839 | Letter |
| T | 0.3580 | 9.093 | Letter |
| 23/64" | 0.3594 | 9.128 | Fractional |
| U | 0.3680 | 9.347 | Letter |
| 3/8" | 0.3750 | 9.525 | Fractional |
| V | 0.3770 | 9.576 | Letter |
| W | 0.3860 | 9.804 | Letter |
| 25/64" | 0.3906 | 9.922 | Fractional |
| X | 0.3970 | 10.084 | Letter |
| Y | 0.4040 | 10.262 | Letter |
| 13/32" | 0.4062 | 10.319 | Fractional |
| Z | 0.4130 | 10.490 | Letter |
| 27/64" | 0.4219 | 10.716 | Fractional |
| 7/16" | 0.4375 | 11.112 | Fractional |
| 29/64" | 0.4531 | 11.509 | Fractional |
| 15/32" | 0.4688 | 11.906 | Fractional |
| 31/64" | 0.4844 | 12.303 | Fractional |
| 1/2" | 0.5000 | 12.700 | Fractional |
Standard fractional drill bits measured in inches (e.g., 1/16", 1/8", 1/4").
Most common for general drilling
Numbered drill bits from #80 (0.0135") to #1 (0.2280").
Ideal for precision small holes
Letter drill bits from A (0.2340") to Z (0.4130").
Perfect for tap drill applications
Our CNC machining services include precision drilling operations with tight tolerances and superior surface finishes.