Number drill chart
Number (wire gauge) drill sizes from #1 down to #80, with decimal-inch and millimeter equivalents. The number series covers the small holes below a quarter inch, with the size getting smaller as the number gets larger.
Number drill sizes
| Number | 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 | 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 |
Number drills run counter to intuition: #1 is the largest at 0.228 inch and #80 the smallest at 0.0135 inch. They fill the fine range below 1/4 inch where fractional steps are too coarse, and many are standard tap drills, such as #7 for a 1/4-20 thread. The series interleaves with the letter and fractional drills for full coverage.
Looking up a tap drill or other sizes?
See the full Drill Size Chart for fractional and letter sizes, or the Tap Drill Calculator for threaded holes.
Why the numbers run backward
The number drill series follows the old wire gauge system, where a higher gauge number means a thinner wire and so a smaller drill. That is why #1 is the biggest and #80 the smallest. It feels backward next to fractional sizes, but the chart makes the actual diameter clear in decimal inches.
Number drills as tap drills
Many number drills are the exact tap drill for a common thread. A #7 (0.201 in) is used for 1/4-20, a #29 (0.136 in) for 8-32, and a #21 (0.159 in) for 10-24. Because these fall between fractional sizes, the number series is essential for cutting threads to the right percentage of engagement.
FAQ
Is #1 or #80 the bigger drill?
#1 is the largest number drill at 0.228 inch; #80 is the smallest at 0.0135 inch. The diameter shrinks as the number rises.
What number drill is used for 1/4-20?
A #7 drill, 0.201 inch, is the standard tap drill for a 1/4-20 thread, giving about 75 percent thread engagement.
What is the smallest number drill?
#80, at 0.0135 inch (0.343 mm), the finest in the standard number series.