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Drill Bit Size Chart
Quick answer: Four series are in common use — fractional (1/64″ steps), number (#1–#80, largest to smallest), letter (A–Z, smallest to largest) and metric. The master chart below merges all four into one list sorted by real diameter.
Most drill charts make you jump between four tables to answer one question: what is the next size up from a #29? This puts every fractional, number, letter and metric bit in a single column sorted by actual diameter.
Master drill size chart — all series, sorted by diameter
Every standard drill size from 0.0135″ to 1″, in ascending order. Where a row shows more than one label those bits are the same diameter — letter E and a 1/4″ bit cut the same hole. The millimetre column is the exact conversion, not a nearest stock size.
| Decimal (in) | Fraction | Number / Letter | Metric | mm |
|---|---|---|---|---|
| 0.0135 | #80 | 0.343 | ||
| 0.0145 | #79 | 0.368 | ||
| 0.0156 | 1/64" | 0.396 | ||
| 0.0160 | #78 | 0.406 | ||
| 0.0180 | #77 | 0.457 | ||
| 0.0197 | 0.5 mm | 0.500 | ||
| 0.0200 | #76 | 0.508 | ||
| 0.0210 | #75 | 0.533 | ||
| 0.0225 | #74 | 0.571 | ||
| 0.0236 | 0.6 mm | 0.599 | ||
| 0.0240 | #73 | 0.610 | ||
| 0.0250 | #72 | 0.635 | ||
| 0.0260 | #71 | 0.660 | ||
| 0.0276 | 0.7 mm | 0.701 | ||
| 0.0280 | #70 | 0.711 | ||
| 0.0292 | #69 | 0.742 | ||
| 0.0310 | #68 | 0.787 | ||
| 0.0312 | 1/32" | 0.792 | ||
| 0.0315 | 0.8 mm | 0.800 | ||
| 0.0320 | #67 | 0.813 | ||
| 0.0330 | #66 | 0.838 | ||
| 0.0350 | #65 | 0.889 | ||
| 0.0354 | 0.9 mm | 0.899 | ||
| 0.0360 | #64 | 0.914 | ||
| 0.0370 | #63 | 0.940 | ||
| 0.0380 | #62 | 0.965 | ||
| 0.0390 | #61 | 0.991 | ||
| 0.0394 | 1 mm | 1.001 | ||
| 0.0400 | #60 | 1.016 | ||
| 0.0410 | #59 | 1.041 | ||
| 0.0420 | #58 | 1.067 | ||
| 0.0430 | #57 | 1.092 | ||
| 0.0433 | 1.1 mm | 1.100 | ||
| 0.0465 | #56 | 1.181 | ||
| 0.0469 | 3/64" | 1.191 | ||
| 0.0472 | 1.2 mm | 1.199 | ||
| 0.0512 | 1.3 mm | 1.300 | ||
| 0.0520 | #55 | 1.321 | ||
| 0.0550 | #54 | 1.397 | ||
| 0.0551 | 1.4 mm | 1.400 | ||
| 0.0591 | 1.5 mm | 1.501 | ||
| 0.0595 | #53 | 1.511 | ||
| 0.0625 | 1/16" | 1.587 | ||
| 0.0630 | 1.6 mm | 1.600 | ||
| 0.0635 | #52 | 1.613 | ||
| 0.0669 | 1.7 mm | 1.699 | ||
| 0.0670 | #51 | 1.702 | ||
| 0.0700 | #50 | 1.778 | ||
| 0.0709 | 1.8 mm | 1.801 | ||
| 0.0730 | #49 | 1.854 | ||
| 0.0748 | 1.9 mm | 1.900 | ||
| 0.0760 | #48 | 1.930 | ||
| 0.0781 | 5/64" | 1.984 | ||
| 0.0785 | #47 | 1.994 | ||
| 0.0787 | 2 mm | 1.999 | ||
| 0.0810 | #46 | 2.057 | ||
| 0.0820 | #45 | 2.083 | ||
| 0.0827 | 2.1 mm | 2.101 | ||
| 0.0860 | #44 | 2.184 | ||
| 0.0866 | 2.2 mm | 2.200 | ||
| 0.0890 | #43 | 2.261 | ||
| 0.0906 | 2.3 mm | 2.301 | ||
| 0.0935 | #42 | 2.375 | ||
| 0.0938 | 3/32" | 2.383 | ||
| 0.0945 | 2.4 mm | 2.400 | ||
| 0.0960 | #41 | 2.438 | ||
| 0.0980 | #40 | 2.489 | ||
| 0.0984 | 2.5 mm | 2.499 | ||
| 0.0995 | #39 | 2.527 | ||
| 0.1015 | #38 | 2.578 | ||
| 0.1024 | 2.6 mm | 2.601 | ||
| 0.1040 | #37 | 2.642 | ||
| 0.1063 | 2.7 mm | 2.700 | ||
| 0.1065 | #36 | 2.705 | ||
| 0.1094 | 7/64" | 2.779 | ||
| 0.1100 | #35 | 2.794 | ||
| 0.1102 | 2.8 mm | 2.799 | ||
| 0.1110 | #34 | 2.819 | ||
| 0.1130 | #33 | 2.870 | ||
| 0.1142 | 2.9 mm | 2.901 | ||
| 0.1160 | #32 | 2.946 | ||
| 0.1181 | 3 mm | 3.000 | ||
| 0.1200 | #31 | 3.048 | ||
| 0.1220 | 3.1 mm | 3.099 | ||
| 0.1250 | 1/8" | 3.175 | ||
| 0.1260 | 3.2 mm | 3.200 | ||
| 0.1285 | #30 | 3.264 | ||
| 0.1299 | 3.3 mm | 3.299 | ||
| 0.1339 | 3.4 mm | 3.401 | ||
| 0.1360 | #29 | 3.454 | ||
| 0.1378 | 3.5 mm | 3.500 | ||
| 0.1405 | #28 | 3.569 | ||
| 0.1406 | 9/64" | 3.571 | ||
| 0.1417 | 3.6 mm | 3.599 | ||
| 0.1440 | #27 | 3.658 | ||
| 0.1457 | 3.7 mm | 3.701 | ||
| 0.1470 | #26 | 3.734 | ||
| 0.1495 | #25 | 3.797 | ||
| 0.1496 | 3.8 mm | 3.800 | ||
| 0.1520 | #24 | 3.861 | ||
| 0.1535 | 3.9 mm | 3.899 | ||
| 0.1540 | #23 | 3.912 | ||
| 0.1562 | 5/32" | 3.967 | ||
| 0.1570 | #22 | 3.988 | ||
| 0.1575 | 4 mm | 4.000 | ||
| 0.1590 | #21 | 4.039 | ||
| 0.1610 | #20 | 4.089 | ||
| 0.1654 | 4.2 mm | 4.201 | ||
| 0.1660 | #19 | 4.216 | ||
| 0.1695 | #18 | 4.305 | ||
| 0.1719 | 11/64" | 4.366 | ||
| 0.1730 | #17 | 4.394 | ||
| 0.1770 | #16 | 4.496 | ||
| 0.1772 | 4.5 mm | 4.501 | ||
| 0.1800 | #15 | 4.572 | ||
| 0.1820 | #14 | 4.623 | ||
| 0.1850 | #13 | 4.699 | ||
| 0.1875 | 3/16" | 4.762 | ||
| 0.1890 | #12 | 4.8 mm | 4.801 | |
| 0.1910 | #11 | 4.851 | ||
| 0.1935 | #10 | 4.915 | ||
| 0.1960 | #9 | 4.978 | ||
| 0.1969 | 5 mm | 5.001 | ||
| 0.1990 | #8 | 5.055 | ||
| 0.2010 | #7 | 5.105 | ||
| 0.2031 | 13/64" | 5.159 | ||
| 0.2040 | #6 | 5.182 | ||
| 0.2047 | 5.2 mm | 5.199 | ||
| 0.2055 | #5 | 5.220 | ||
| 0.2090 | #4 | 5.309 | ||
| 0.2130 | #3 | 5.410 | ||
| 0.2165 | 5.5 mm | 5.499 | ||
| 0.2188 | 7/32" | 5.558 | ||
| 0.2210 | #2 | 5.613 | ||
| 0.2280 | #1 | 5.791 | ||
| 0.2283 | 5.8 mm | 5.799 | ||
| 0.2340 | A | 5.944 | ||
| 0.2344 | 15/64" | 5.954 | ||
| 0.2362 | 6 mm | 5.999 | ||
| 0.2380 | B | 6.045 | ||
| 0.2420 | C | 6.147 | ||
| 0.2441 | 6.2 mm | 6.200 | ||
| 0.2460 | D | 6.248 | ||
| 0.2500 | 1/4" | E | 6.350 | |
| 0.2559 | 6.5 mm | 6.500 | ||
| 0.2570 | F | 6.528 | ||
| 0.2610 | G | 6.629 | ||
| 0.2656 | 17/64" | 6.746 | ||
| 0.2660 | H | 6.756 | ||
| 0.2677 | 6.8 mm | 6.800 | ||
| 0.2720 | I | 6.909 | ||
| 0.2756 | 7 mm | 7.000 | ||
| 0.2770 | J | 7.036 | ||
| 0.2810 | K | 7.137 | ||
| 0.2812 | 9/32" | 7.142 | ||
| 0.2835 | 7.2 mm | 7.201 | ||
| 0.2900 | L | 7.366 | ||
| 0.2950 | M | 7.493 | ||
| 0.2953 | 7.5 mm | 7.501 | ||
| 0.2969 | 19/64" | 7.541 | ||
| 0.3020 | N | 7.671 | ||
| 0.3071 | 7.8 mm | 7.800 | ||
| 0.3125 | 5/16" | 7.938 | ||
| 0.3150 | 8 mm | 8.001 | ||
| 0.3160 | O | 8.026 | ||
| 0.3228 | 8.2 mm | 8.199 | ||
| 0.3230 | P | 8.204 | ||
| 0.3281 | 21/64" | 8.334 | ||
| 0.3320 | Q | 8.433 | ||
| 0.3346 | 8.5 mm | 8.499 | ||
| 0.3390 | R | 8.611 | ||
| 0.3438 | 11/32" | 8.733 | ||
| 0.3465 | 8.8 mm | 8.801 | ||
| 0.3480 | S | 8.839 | ||
| 0.3543 | 9 mm | 8.999 | ||
| 0.3580 | T | 9.093 | ||
| 0.3594 | 23/64" | 9.129 | ||
| 0.3622 | 9.2 mm | 9.200 | ||
| 0.3680 | U | 9.347 | ||
| 0.3740 | 9.5 mm | 9.500 | ||
| 0.3750 | 3/8" | 9.525 | ||
| 0.3770 | V | 9.576 | ||
| 0.3858 | 9.8 mm | 9.799 | ||
| 0.3860 | W | 9.804 | ||
| 0.3906 | 25/64" | 9.921 | ||
| 0.3937 | 10 mm | 10.000 | ||
| 0.3970 | X | 10.084 | ||
| 0.4016 | 10.2 mm | 10.201 | ||
| 0.4040 | Y | 10.262 | ||
| 0.4062 | 13/32" | 10.317 | ||
| 0.4130 | Z | 10.490 | ||
| 0.4134 | 10.5 mm | 10.500 | ||
| 0.4219 | 27/64" | 10.716 | ||
| 0.4331 | 11 mm | 11.001 | ||
| 0.4375 | 7/16" | 11.112 | ||
| 0.4528 | 11.5 mm | 11.501 | ||
| 0.4531 | 29/64" | 11.509 | ||
| 0.4688 | 15/32" | 11.908 | ||
| 0.4724 | 12 mm | 11.999 | ||
| 0.4844 | 31/64" | 12.304 | ||
| 0.4921 | 12.5 mm | 12.499 | ||
| 0.5000 | 1/2" | 12.700 | ||
| 0.5118 | 13 mm | 13.000 | ||
| 0.5156 | 33/64" | 13.096 | ||
| 0.5312 | 17/32" | 13.492 | ||
| 0.5469 | 35/64" | 13.891 | ||
| 0.5512 | 14 mm | 14.000 | ||
| 0.5625 | 9/16" | 14.287 | ||
| 0.5781 | 37/64" | 14.684 | ||
| 0.5906 | 15 mm | 15.001 | ||
| 0.5938 | 19/32" | 15.083 | ||
| 0.6094 | 39/64" | 15.479 | ||
| 0.6250 | 5/8" | 15.875 | ||
| 0.6299 | 16 mm | 15.999 | ||
| 0.6406 | 41/64" | 16.271 | ||
| 0.6562 | 21/32" | 16.667 | ||
| 0.6693 | 17 mm | 17.000 | ||
| 0.6719 | 43/64" | 17.066 | ||
| 0.6875 | 11/16" | 17.462 | ||
| 0.7031 | 45/64" | 17.859 | ||
| 0.7087 | 18 mm | 18.001 | ||
| 0.7188 | 23/32" | 18.258 | ||
| 0.7344 | 47/64" | 18.654 | ||
| 0.7480 | 19 mm | 18.999 | ||
| 0.7500 | 3/4" | 19.050 | ||
| 0.7656 | 49/64" | 19.446 | ||
| 0.7812 | 25/32" | 19.842 | ||
| 0.7874 | 20 mm | 20.000 | ||
| 0.7969 | 51/64" | 20.241 | ||
| 0.8125 | 13/16" | 20.637 | ||
| 0.8268 | 21 mm | 21.001 | ||
| 0.8281 | 53/64" | 21.034 | ||
| 0.8438 | 27/32" | 21.433 | ||
| 0.8594 | 55/64" | 21.829 | ||
| 0.8661 | 22 mm | 21.999 | ||
| 0.8750 | 7/8" | 22.225 | ||
| 0.8906 | 57/64" | 22.621 | ||
| 0.9055 | 23 mm | 23.000 | ||
| 0.9062 | 29/32" | 23.017 | ||
| 0.9219 | 59/64" | 23.416 | ||
| 0.9375 | 15/16" | 23.812 | ||
| 0.9449 | 24 mm | 24.000 | ||
| 0.9531 | 61/64" | 24.209 | ||
| 0.9688 | 31/32" | 24.608 | ||
| 0.9843 | 25 mm | 25.001 | ||
| 0.9844 | 63/64" | 25.004 | ||
| 1.0000 | 1" | 25.400 |
247 distinct diameters. Values are the nominal diameters given in the standard; a new bit is typically within ±0.0005″ of nominal, a resharpened one is not.
Fractional drill sizes (1/64″ to 1″)
The set almost everyone owns. Steps are 1/64″ — 0.0156″, about 15.6 thou — which is coarse enough that for threading and press fits you usually need a number or letter bit instead.
| Fraction | Decimal (in) | mm |
|---|---|---|
| 1/64" | 0.0156 | 0.397 |
| 1/32" | 0.0312 | 0.794 |
| 3/64" | 0.0469 | 1.191 |
| 1/16" | 0.0625 | 1.587 |
| 5/64" | 0.0781 | 1.984 |
| 3/32" | 0.0938 | 2.381 |
| 7/64" | 0.1094 | 2.778 |
| 1/8" | 0.1250 | 3.175 |
| 9/64" | 0.1406 | 3.572 |
| 5/32" | 0.1562 | 3.969 |
| 11/64" | 0.1719 | 4.366 |
| 3/16" | 0.1875 | 4.762 |
| 13/64" | 0.2031 | 5.159 |
| 7/32" | 0.2188 | 5.556 |
| 15/64" | 0.2344 | 5.953 |
| 1/4" | 0.2500 | 6.350 |
| 17/64" | 0.2656 | 6.747 |
| 9/32" | 0.2812 | 7.144 |
| 19/64" | 0.2969 | 7.541 |
| 5/16" | 0.3125 | 7.938 |
| 21/64" | 0.3281 | 8.334 |
| 11/32" | 0.3438 | 8.731 |
| 23/64" | 0.3594 | 9.128 |
| 3/8" | 0.3750 | 9.525 |
| 25/64" | 0.3906 | 9.922 |
| 13/32" | 0.4062 | 10.319 |
| 27/64" | 0.4219 | 10.716 |
| 7/16" | 0.4375 | 11.112 |
| 29/64" | 0.4531 | 11.509 |
| 15/32" | 0.4688 | 11.906 |
| 31/64" | 0.4844 | 12.303 |
| 1/2" | 0.5000 | 12.700 |
| 33/64" | 0.5156 | 13.097 |
| 17/32" | 0.5312 | 13.494 |
| 35/64" | 0.5469 | 13.891 |
| 9/16" | 0.5625 | 14.287 |
| 37/64" | 0.5781 | 14.684 |
| 19/32" | 0.5938 | 15.081 |
| 39/64" | 0.6094 | 15.478 |
| 5/8" | 0.6250 | 15.875 |
| 41/64" | 0.6406 | 16.272 |
| 21/32" | 0.6562 | 16.669 |
| 43/64" | 0.6719 | 17.066 |
| 11/16" | 0.6875 | 17.462 |
| 45/64" | 0.7031 | 17.859 |
| 23/32" | 0.7188 | 18.256 |
| 47/64" | 0.7344 | 18.653 |
| 3/4" | 0.7500 | 19.050 |
| 49/64" | 0.7656 | 19.447 |
| 25/32" | 0.7812 | 19.844 |
| 51/64" | 0.7969 | 20.241 |
| 13/16" | 0.8125 | 20.637 |
| 53/64" | 0.8281 | 21.034 |
| 27/32" | 0.8438 | 21.431 |
| 55/64" | 0.8594 | 21.828 |
| 7/8" | 0.8750 | 22.225 |
| 57/64" | 0.8906 | 22.622 |
| 29/32" | 0.9062 | 23.019 |
| 59/64" | 0.9219 | 23.416 |
| 15/16" | 0.9375 | 23.812 |
| 61/64" | 0.9531 | 24.209 |
| 31/32" | 0.9688 | 24.606 |
| 63/64" | 0.9844 | 25.003 |
| 1" | 1.0000 | 25.400 |
Number (wire gauge) drill sizes, #1 to #80
Counter-intuitive but consistent: the bigger the number, the smaller the bit. #1 is 0.228″ and #80 is 0.0135″. This series is where nearly every imperial tap drill lives.
#1 through #40
| Size | Decimal (in) | mm |
|---|---|---|
| #1 | 0.2280 | 5.791 |
| #2 | 0.2210 | 5.613 |
| #3 | 0.2130 | 5.410 |
| #4 | 0.2090 | 5.309 |
| #5 | 0.2055 | 5.220 |
| #6 | 0.2040 | 5.182 |
| #7 | 0.2010 | 5.105 |
| #8 | 0.1990 | 5.055 |
| #9 | 0.1960 | 4.978 |
| #10 | 0.1935 | 4.915 |
| #11 | 0.1910 | 4.851 |
| #12 | 0.1890 | 4.801 |
| #13 | 0.1850 | 4.699 |
| #14 | 0.1820 | 4.623 |
| #15 | 0.1800 | 4.572 |
| #16 | 0.1770 | 4.496 |
| #17 | 0.1730 | 4.394 |
| #18 | 0.1695 | 4.305 |
| #19 | 0.1660 | 4.216 |
| #20 | 0.1610 | 4.089 |
| #21 | 0.1590 | 4.039 |
| #22 | 0.1570 | 3.988 |
| #23 | 0.1540 | 3.912 |
| #24 | 0.1520 | 3.861 |
| #25 | 0.1495 | 3.797 |
| #26 | 0.1470 | 3.734 |
| #27 | 0.1440 | 3.658 |
| #28 | 0.1405 | 3.569 |
| #29 | 0.1360 | 3.454 |
| #30 | 0.1285 | 3.264 |
| #31 | 0.1200 | 3.048 |
| #32 | 0.1160 | 2.946 |
| #33 | 0.1130 | 2.870 |
| #34 | 0.1110 | 2.819 |
| #35 | 0.1100 | 2.794 |
| #36 | 0.1065 | 2.705 |
| #37 | 0.1040 | 2.642 |
| #38 | 0.1015 | 2.578 |
| #39 | 0.0995 | 2.527 |
| #40 | 0.0980 | 2.489 |
#41 through #80
| Size | Decimal (in) | mm |
|---|---|---|
| #41 | 0.0960 | 2.438 |
| #42 | 0.0935 | 2.375 |
| #43 | 0.0890 | 2.261 |
| #44 | 0.0860 | 2.184 |
| #45 | 0.0820 | 2.083 |
| #46 | 0.0810 | 2.057 |
| #47 | 0.0785 | 1.994 |
| #48 | 0.0760 | 1.930 |
| #49 | 0.0730 | 1.854 |
| #50 | 0.0700 | 1.778 |
| #51 | 0.0670 | 1.702 |
| #52 | 0.0635 | 1.613 |
| #53 | 0.0595 | 1.511 |
| #54 | 0.0550 | 1.397 |
| #55 | 0.0520 | 1.321 |
| #56 | 0.0465 | 1.181 |
| #57 | 0.0430 | 1.092 |
| #58 | 0.0420 | 1.067 |
| #59 | 0.0410 | 1.041 |
| #60 | 0.0400 | 1.016 |
| #61 | 0.0390 | 0.991 |
| #62 | 0.0380 | 0.965 |
| #63 | 0.0370 | 0.940 |
| #64 | 0.0360 | 0.914 |
| #65 | 0.0350 | 0.889 |
| #66 | 0.0330 | 0.838 |
| #67 | 0.0320 | 0.813 |
| #68 | 0.0310 | 0.787 |
| #69 | 0.0292 | 0.742 |
| #70 | 0.0280 | 0.711 |
| #71 | 0.0260 | 0.660 |
| #72 | 0.0250 | 0.635 |
| #73 | 0.0240 | 0.610 |
| #74 | 0.0225 | 0.571 |
| #75 | 0.0210 | 0.533 |
| #76 | 0.0200 | 0.508 |
| #77 | 0.0180 | 0.457 |
| #78 | 0.0160 | 0.406 |
| #79 | 0.0145 | 0.368 |
| #80 | 0.0135 | 0.343 |
Letter drill sizes, A to Z
Runs the opposite way to the number series — A is smallest at 0.234″, Z largest at 0.413″. Letters pick up exactly where #1 (0.228″) leaves off and cover the range just above 1/4″, otherwise a dead zone between fractional sizes.
| Size | Decimal (in) | mm |
|---|---|---|
| A | 0.2340 | 5.944 |
| B | 0.2380 | 6.045 |
| C | 0.2420 | 6.147 |
| D | 0.2460 | 6.248 |
| E | 0.2500 | 6.350 |
| F | 0.2570 | 6.528 |
| G | 0.2610 | 6.629 |
| H | 0.2660 | 6.756 |
| I | 0.2720 | 6.909 |
| J | 0.2770 | 7.036 |
| K | 0.2810 | 7.137 |
| L | 0.2900 | 7.366 |
| M | 0.2950 | 7.493 |
| N | 0.3020 | 7.671 |
| O | 0.3160 | 8.026 |
| P | 0.3230 | 8.204 |
| Q | 0.3320 | 8.433 |
| R | 0.3390 | 8.611 |
| S | 0.3480 | 8.839 |
| T | 0.3580 | 9.093 |
| U | 0.3680 | 9.347 |
| V | 0.3770 | 9.576 |
| W | 0.3860 | 9.804 |
| X | 0.3970 | 10.084 |
| Y | 0.4040 | 10.262 |
| Z | 0.4130 | 10.490 |
Metric drill sizes and their inch equivalents
The right-hand column gives the nearest fractional bit and how far off it is, in thousandths of an inch. Under about five thou you can usually substitute; over that you will feel it in a fit.
| Metric | Decimal (in) | Nearest fractional bit |
|---|---|---|
| 0.5 mm | 0.0197 | 1/64" (+4.1 thou) |
| 0.6 mm | 0.0236 | 1/32" (-7.6 thou) |
| 0.7 mm | 0.0276 | 1/32" (-3.7 thou) |
| 0.8 mm | 0.0315 | 1/32" (+0.2 thou) |
| 0.9 mm | 0.0354 | 1/32" (+4.2 thou) |
| 1 mm | 0.0394 | 3/64" (-7.5 thou) |
| 1.1 mm | 0.0433 | 3/64" (-3.6 thou) |
| 1.2 mm | 0.0472 | 3/64" (+0.4 thou) |
| 1.3 mm | 0.0512 | 3/64" (+4.3 thou) |
| 1.4 mm | 0.0551 | 1/16" (-7.4 thou) |
| 1.5 mm | 0.0591 | 1/16" (-3.4 thou) |
| 1.6 mm | 0.0630 | 1/16" (+0.5 thou) |
| 1.7 mm | 0.0669 | 1/16" (+4.4 thou) |
| 1.8 mm | 0.0709 | 5/64" (-7.3 thou) |
| 1.9 mm | 0.0748 | 5/64" (-3.3 thou) |
| 2 mm | 0.0787 | 5/64" (+0.6 thou) |
| 2.1 mm | 0.0827 | 5/64" (+4.6 thou) |
| 2.2 mm | 0.0866 | 3/32" (-7.1 thou) |
| 2.3 mm | 0.0906 | 3/32" (-3.2 thou) |
| 2.4 mm | 0.0945 | 3/32" (+0.7 thou) |
| 2.5 mm | 0.0984 | 3/32" (+4.7 thou) |
| 2.6 mm | 0.1024 | 7/64" (-7.0 thou) |
| 2.7 mm | 0.1063 | 7/64" (-3.1 thou) |
| 2.8 mm | 0.1102 | 7/64" (+0.9 thou) |
| 2.9 mm | 0.1142 | 7/64" (+4.8 thou) |
| 3 mm | 0.1181 | 1/8" (-6.9 thou) |
| 3.1 mm | 0.1220 | 1/8" (-3.0 thou) |
| 3.2 mm | 0.1260 | 1/8" (+1.0 thou) |
| 3.3 mm | 0.1299 | 1/8" (+4.9 thou) |
| 3.4 mm | 0.1339 | 9/64" (-6.8 thou) |
| 3.5 mm | 0.1378 | 9/64" (-2.8 thou) |
| 3.6 mm | 0.1417 | 9/64" (+1.1 thou) |
| 3.7 mm | 0.1457 | 9/64" (+5.0 thou) |
| 3.8 mm | 0.1496 | 5/32" (-6.6 thou) |
| 3.9 mm | 0.1535 | 5/32" (-2.7 thou) |
| 4 mm | 0.1575 | 5/32" (+1.2 thou) |
| 4.2 mm | 0.1654 | 11/64" (-6.5 thou) |
| 4.5 mm | 0.1772 | 11/64" (+5.3 thou) |
| 4.8 mm | 0.1890 | 3/16" (+1.5 thou) |
| 5 mm | 0.1969 | 13/64" (-6.3 thou) |
| 5.2 mm | 0.2047 | 13/64" (+1.6 thou) |
| 5.5 mm | 0.2165 | 7/32" (-2.2 thou) |
| 5.8 mm | 0.2283 | 15/64" (-6.0 thou) |
| 6 mm | 0.2362 | 15/64" (+1.8 thou) |
| 6.2 mm | 0.2441 | 1/4" (-5.9 thou) |
| 6.5 mm | 0.2559 | 1/4" (+5.9 thou) |
| 6.8 mm | 0.2677 | 17/64" (+2.1 thou) |
| 7 mm | 0.2756 | 9/32" (-5.7 thou) |
| 7.2 mm | 0.2835 | 9/32" (+2.2 thou) |
| 7.5 mm | 0.2953 | 19/64" (-1.6 thou) |
| 7.8 mm | 0.3071 | 5/16" (-5.4 thou) |
| 8 mm | 0.3150 | 5/16" (+2.5 thou) |
| 8.2 mm | 0.3228 | 21/64" (-5.3 thou) |
| 8.5 mm | 0.3346 | 21/64" (+6.5 thou) |
| 8.8 mm | 0.3465 | 11/32" (+2.7 thou) |
| 9 mm | 0.3543 | 23/64" (-5.0 thou) |
| 9.2 mm | 0.3622 | 23/64" (+2.8 thou) |
| 9.5 mm | 0.3740 | 3/8" (-1.0 thou) |
| 9.8 mm | 0.3858 | 25/64" (-4.8 thou) |
| 10 mm | 0.3937 | 25/64" (+3.1 thou) |
| 10.2 mm | 0.4016 | 13/32" (-4.7 thou) |
| 10.5 mm | 0.4134 | 13/32" (+7.1 thou) |
| 11 mm | 0.4331 | 7/16" (-4.4 thou) |
| 11.5 mm | 0.4528 | 29/64" (-0.4 thou) |
| 12 mm | 0.4724 | 15/32" (+3.7 thou) |
| 12.5 mm | 0.4921 | 31/64" (+7.8 thou) |
| 13 mm | 0.5118 | 33/64" (-3.8 thou) |
| 14 mm | 0.5512 | 35/64" (+4.3 thou) |
| 15 mm | 0.5906 | 19/32" (-3.2 thou) |
| 16 mm | 0.6299 | 5/8" (+4.9 thou) |
| 17 mm | 0.6693 | 43/64" (-2.6 thou) |
| 18 mm | 0.7087 | 45/64" (+5.5 thou) |
| 19 mm | 0.7480 | 3/4" (-2.0 thou) |
| 20 mm | 0.7874 | 25/32" (+6.2 thou) |
| 21 mm | 0.8268 | 53/64" (-1.4 thou) |
| 22 mm | 0.8661 | 55/64" (+6.8 thou) |
| 23 mm | 0.9055 | 29/32" (-0.7 thou) |
| 24 mm | 0.9449 | 15/16" (+7.4 thou) |
| 25 mm | 0.9843 | 63/64" (-0.1 thou) |
How to pick the right bit
Clearance hole for a bolt
The hole wants to be slightly larger than the fastener so the bolt drops through without binding. For a 1/4″ bolt that is 17/64″ close fit or 9/32″ free fit — never 1/4″ itself. Full table on the tap and clearance drill chart.
Hole to be tapped
The hole must be smaller than the thread’s major diameter by roughly the pitch, which is why tap drills are nearly always number or letter sizes. A 1/4-20 thread takes a #7 (0.201″), not a 3/16″ or a 1/4″.
Wood screw
Two holes, not one: a pilot in the receiving piece sized to the screw’s root diameter, and a clearance hole through the top piece sized to the shank. Sizes by gauge are on the pilot hole chart.
Identifying an unmarked bit
Worn markings are the usual reason people reach for a chart like this. Measure across the two cutting lips with a caliper — not across the flutes, which read undersize because of the relief grind — then find the closest decimal in the master table. If your reading falls between two listed sizes, the bit is almost certainly the larger of the two, resharpened.
Frequently asked questions
What size is a #29 drill bit?
0.1360 in (3.454 mm). It is the standard tap drill for an 8-32 thread, which is why it is one of the most-used bits in the number set.
What is the difference between number, letter and fractional drill bits?
They are three overlapping series that fill the gaps between fractional sizes. Fractional bits step in 1/64 in jumps. Number bits (#1 to #80) run 0.2280 in down to 0.0135 in in much finer steps. Letter bits (A to Z) cover 0.234 to 0.413 in, bridging the gap just above 1/4 in. Together they give roughly 0.003 in resolution where fractional bits alone give 0.0156 in.
What letter drill is closest to 1/4 inch?
Letter E is exactly 0.250 in — the same as a 1/4 in fractional bit. Letter D (0.246 in) is the next size down and F (0.257 in) the next up.
Is a 3/8 drill bit the same as 10mm?
No, but they are close. 3/8 in is 9.525 mm, so a 10 mm bit cuts a hole 0.475 mm — about 19 thousandths — larger. That is enough to matter for a press fit and enough to leave a bolt sloppy in a clearance hole.
What is the smallest standard drill bit?
In the number series, #80 at 0.0135 in (0.343 mm). Below that you are into micro drills sized directly in thousandths or millimetres.