Drill bit sizes
Three systems of drill size overlap across the same range of holes, and a bit marked 7 or F or 21/64 gives no clue which one it belongs to. All 150 of them are here, each with its own page giving the size in inches and millimetres, the nearest bit in the other two systems, and the tap it is cut for.
The trap in the number system
Number drills get smaller as the number gets larger. #1 is 0.228 inches and #60 is 0.04 — an index, not a measurement. Letter drills do the opposite and grow from A to Z. Fractional drills are the only ones where the marking is the size, and they are also the coarsest, which is why the other two exist.
The one overlap
E and 1/4 inch are the same drill, both exactly 0.250 inches. It is the only place in the three systems where a letter and a fraction land on the same diameter.
Number drills, #1 to #60
The fine end of the imperial range, and where most tapping drills live. Remember that the numbers run backwards.
| Drill | Inches | Millimetres | Tap |
|---|---|---|---|
| #60 | 0.04 in | 1.02 mm | — |
| #59 | 0.041 in | 1.04 mm | — |
| #58 | 0.042 in | 1.07 mm | — |
| #57 | 0.043 in | 1.09 mm | — |
| #56 | 0.0465 in | 1.18 mm | — |
| #55 | 0.052 in | 1.32 mm | — |
| #54 | 0.055 in | 1.4 mm | — |
| #53 | 0.0595 in | 1.51 mm | 1-64, 1-72 |
| #52 | 0.0635 in | 1.61 mm | — |
| #51 | 0.067 in | 1.7 mm | — |
| #50 | 0.07 in | 1.78 mm | 2-56, 2-64 |
| #49 | 0.073 in | 1.85 mm | — |
| #48 | 0.076 in | 1.93 mm | — |
| #47 | 0.0785 in | 1.99 mm | 3-48 |
| #46 | 0.081 in | 2.06 mm | — |
| #45 | 0.082 in | 2.08 mm | 3-56 |
| #44 | 0.086 in | 2.18 mm | — |
| #43 | 0.089 in | 2.26 mm | 4-40 |
| #42 | 0.0935 in | 2.37 mm | 4-48 |
| #41 | 0.096 in | 2.44 mm | — |
| #40 | 0.098 in | 2.49 mm | — |
| #39 | 0.0995 in | 2.53 mm | — |
| #38 | 0.1015 in | 2.58 mm | 5-40 |
| #37 | 0.104 in | 2.64 mm | 5-44 |
| #36 | 0.1065 in | 2.71 mm | 6-32 |
| #35 | 0.11 in | 2.79 mm | — |
| #34 | 0.111 in | 2.82 mm | — |
| #33 | 0.113 in | 2.87 mm | 6-40 |
| #32 | 0.116 in | 2.95 mm | — |
| #31 | 0.12 in | 3.05 mm | — |
| #30 | 0.1285 in | 3.26 mm | — |
| #29 | 0.136 in | 3.45 mm | 8-32, 8-36 |
| #28 | 0.1405 in | 3.57 mm | — |
| #27 | 0.144 in | 3.66 mm | — |
| #26 | 0.147 in | 3.73 mm | — |
| #25 | 0.1495 in | 3.8 mm | 10-24 |
| #24 | 0.152 in | 3.86 mm | — |
| #23 | 0.154 in | 3.91 mm | — |
| #22 | 0.157 in | 3.99 mm | — |
| #21 | 0.159 in | 4.04 mm | 10-32 |
| #20 | 0.161 in | 4.09 mm | — |
| #19 | 0.166 in | 4.22 mm | — |
| #18 | 0.1695 in | 4.31 mm | — |
| #17 | 0.173 in | 4.39 mm | — |
| #16 | 0.177 in | 4.5 mm | 12-24 |
| #15 | 0.18 in | 4.57 mm | — |
| #14 | 0.182 in | 4.62 mm | 12-28 |
| #13 | 0.185 in | 4.7 mm | — |
| #12 | 0.189 in | 4.8 mm | — |
| #11 | 0.191 in | 4.85 mm | — |
| #10 | 0.1935 in | 4.91 mm | — |
| #9 | 0.196 in | 4.98 mm | — |
| #8 | 0.199 in | 5.05 mm | — |
| #7 | 0.201 in | 5.11 mm | 1/4-20 |
| #6 | 0.204 in | 5.18 mm | — |
| #5 | 0.2055 in | 5.22 mm | — |
| #4 | 0.209 in | 5.31 mm | — |
| #3 | 0.213 in | 5.41 mm | 1/4-28 |
| #2 | 0.221 in | 5.61 mm | — |
| #1 | 0.228 in | 5.79 mm | — |
Letter drills, A to Z
From 0.234 to 0.413 inches, bridging the largest number drill and the useful fractional sizes.
| Drill | Inches | Millimetres | Tap |
|---|---|---|---|
| A | 0.234 in | 5.94 mm | — |
| B | 0.238 in | 6.05 mm | — |
| C | 0.242 in | 6.15 mm | — |
| D | 0.246 in | 6.25 mm | — |
| E | 0.25 in | 6.35 mm | — |
| F | 0.257 in | 6.53 mm | 5/16-18 |
| G | 0.261 in | 6.63 mm | — |
| H | 0.266 in | 6.76 mm | — |
| I | 0.272 in | 6.91 mm | 5/16-24 |
| J | 0.277 in | 7.04 mm | — |
| K | 0.281 in | 7.14 mm | — |
| L | 0.29 in | 7.37 mm | — |
| M | 0.295 in | 7.49 mm | — |
| N | 0.302 in | 7.67 mm | — |
| O | 0.316 in | 8.03 mm | — |
| P | 0.323 in | 8.2 mm | — |
| Q | 0.332 in | 8.43 mm | 3/8-24 |
| R | 0.339 in | 8.61 mm | — |
| S | 0.348 in | 8.84 mm | — |
| T | 0.358 in | 9.09 mm | — |
| U | 0.368 in | 9.35 mm | 7/16-14 |
| V | 0.377 in | 9.58 mm | — |
| W | 0.386 in | 9.8 mm | — |
| X | 0.397 in | 10.08 mm | — |
| Y | 0.404 in | 10.26 mm | — |
| Z | 0.413 in | 10.49 mm | — |
Fractional drills, 64ths
The set in most homes. Coarse enough that it misses nearly every tapping size, which is the whole reason for the other two systems.
| Drill | Inches | Millimetres | Tap |
|---|---|---|---|
| 1/64" | 0.0156 in | 0.4 mm | — |
| 1/32" | 0.0313 in | 0.79 mm | — |
| 3/64" | 0.0469 in | 1.19 mm | 0-80 |
| 1/16" | 0.0625 in | 1.59 mm | — |
| 5/64" | 0.0781 in | 1.98 mm | — |
| 3/32" | 0.0938 in | 2.38 mm | — |
| 7/64" | 0.1094 in | 2.78 mm | — |
| 1/8" | 0.125 in | 3.18 mm | — |
| 9/64" | 0.1406 in | 3.57 mm | — |
| 5/32" | 0.1563 in | 3.97 mm | — |
| 11/64" | 0.1719 in | 4.37 mm | — |
| 3/16" | 0.1875 in | 4.76 mm | — |
| 13/64" | 0.2031 in | 5.16 mm | — |
| 7/32" | 0.2188 in | 5.56 mm | — |
| 15/64" | 0.2344 in | 5.95 mm | — |
| 1/4" | 0.25 in | 6.35 mm | — |
| 17/64" | 0.2656 in | 6.75 mm | — |
| 9/32" | 0.2813 in | 7.14 mm | — |
| 19/64" | 0.2969 in | 7.54 mm | — |
| 5/16" | 0.3125 in | 7.94 mm | 3/8-16 |
| 21/64" | 0.3281 in | 8.33 mm | — |
| 11/32" | 0.3438 in | 8.73 mm | — |
| 23/64" | 0.3594 in | 9.13 mm | — |
| 3/8" | 0.375 in | 9.52 mm | — |
| 25/64" | 0.3906 in | 9.92 mm | 7/16-20 |
| 13/32" | 0.4063 in | 10.32 mm | — |
| 27/64" | 0.4219 in | 10.72 mm | 1/2-13 |
| 7/16" | 0.4375 in | 11.11 mm | — |
| 29/64" | 0.4531 in | 11.51 mm | 1/2-20 |
| 15/32" | 0.4688 in | 11.91 mm | — |
| 31/64" | 0.4844 in | 12.3 mm | 9/16-12 |
| 1/2" | 0.5 in | 12.7 mm | — |
| 33/64" | 0.5156 in | 13.1 mm | 9/16-18 |
| 17/32" | 0.5313 in | 13.49 mm | 5/8-11 |
| 35/64" | 0.5469 in | 13.89 mm | — |
| 9/16" | 0.5625 in | 14.29 mm | — |
| 37/64" | 0.5781 in | 14.68 mm | 5/8-18 |
| 19/32" | 0.5938 in | 15.08 mm | — |
| 39/64" | 0.6094 in | 15.48 mm | — |
| 5/8" | 0.625 in | 15.88 mm | — |
| 41/64" | 0.6406 in | 16.27 mm | — |
| 21/32" | 0.6563 in | 16.67 mm | 3/4-10 |
| 43/64" | 0.6719 in | 17.07 mm | — |
| 11/16" | 0.6875 in | 17.46 mm | 3/4-16 |
| 45/64" | 0.7031 in | 17.86 mm | — |
| 23/32" | 0.7188 in | 18.26 mm | — |
| 47/64" | 0.7344 in | 18.65 mm | — |
| 3/4" | 0.75 in | 19.05 mm | — |
| 49/64" | 0.7656 in | 19.45 mm | 7/8-9 |
| 25/32" | 0.7813 in | 19.84 mm | — |
| 51/64" | 0.7969 in | 20.24 mm | — |
| 13/16" | 0.8125 in | 20.64 mm | 7/8-14 |
| 53/64" | 0.8281 in | 21.03 mm | — |
| 27/32" | 0.8438 in | 21.43 mm | — |
| 55/64" | 0.8594 in | 21.83 mm | — |
| 7/8" | 0.875 in | 22.23 mm | 1-8 |
| 57/64" | 0.8906 in | 22.62 mm | — |
| 29/32" | 0.9063 in | 23.02 mm | — |
| 59/64" | 0.9219 in | 23.42 mm | 1-12 |
| 15/16" | 0.9375 in | 23.81 mm | — |
| 61/64" | 0.9531 in | 24.21 mm | — |
| 31/32" | 0.9688 in | 24.61 mm | — |
| 63/64" | 0.9844 in | 25 mm | — |
| 1/1" | 1 in | 25.4 mm | — |