Number Drill Bit Sizes (#1 to #80)
Number drills run from #1, the largest at 0.228 inches, down to #80, the smallest at 0.0135 inches. Unlike fractional or metric sizing, a bigger number means a smaller drill: the numbering runs in reverse, which is the single most common point of confusion for anyone new to the system.
Number sizes cover the fine end of the drilling range that fractional bits skip over in bigger steps. Anything smaller than 1/16" (0.0625"), and most small machine-screw tap drills, land on a number size rather than a clean fraction.
Full Number Drill Reference (#1 to #80)
| Number | Decimal (in) | Millimeters |
|---|---|---|
| #1 | 0.2280" | 5.7912 mm |
| #2 | 0.2210" | 5.6134 mm |
| #3 | 0.2130" | 5.4102 mm |
| #4 | 0.2090" | 5.3086 mm |
| #5 | 0.2055" | 5.2197 mm |
| #6 | 0.2040" | 5.1816 mm |
| #7 | 0.2010" | 5.1054 mm |
| #8 | 0.1990" | 5.0546 mm |
| #9 | 0.1960" | 4.9784 mm |
| #10 | 0.1935" | 4.9149 mm |
| #11 | 0.1910" | 4.8514 mm |
| #12 | 0.1890" | 4.8006 mm |
| #13 | 0.1850" | 4.6990 mm |
| #14 | 0.1820" | 4.6228 mm |
| #15 | 0.1800" | 4.5720 mm |
| #16 | 0.1770" | 4.4958 mm |
| #17 | 0.1730" | 4.3942 mm |
| #18 | 0.1695" | 4.3053 mm |
| #19 | 0.1660" | 4.2164 mm |
| #20 | 0.1610" | 4.0894 mm |
| #21 | 0.1590" | 4.0386 mm |
| #22 | 0.1570" | 3.9878 mm |
| #23 | 0.1540" | 3.9116 mm |
| #24 | 0.1520" | 3.8608 mm |
| #25 | 0.1495" | 3.7973 mm |
| #26 | 0.1470" | 3.7338 mm |
| #27 | 0.1440" | 3.6576 mm |
| #28 | 0.1405" | 3.5687 mm |
| #29 | 0.1360" | 3.4544 mm |
| #30 | 0.1285" | 3.2639 mm |
| #31 | 0.1200" | 3.0480 mm |
| #32 | 0.1160" | 2.9464 mm |
| #33 | 0.1130" | 2.8702 mm |
| #34 | 0.1110" | 2.8194 mm |
| #35 | 0.1100" | 2.7940 mm |
| #36 | 0.1065" | 2.7051 mm |
| #37 | 0.1040" | 2.6416 mm |
| #38 | 0.1015" | 2.5781 mm |
| #39 | 0.0995" | 2.5273 mm |
| #40 | 0.0980" | 2.4892 mm |
| #41 | 0.0960" | 2.4384 mm |
| #42 | 0.0935" | 2.3749 mm |
| #43 | 0.0890" | 2.2606 mm |
| #44 | 0.0860" | 2.1844 mm |
| #45 | 0.0820" | 2.0828 mm |
| #46 | 0.0810" | 2.0574 mm |
| #47 | 0.0785" | 1.9939 mm |
| #48 | 0.0760" | 1.9304 mm |
| #49 | 0.0730" | 1.8542 mm |
| #50 | 0.0700" | 1.7780 mm |
| #51 | 0.0670" | 1.7018 mm |
| #52 | 0.0635" | 1.6129 mm |
| #53 | 0.0595" | 1.5113 mm |
| #54 | 0.0550" | 1.3970 mm |
| #55 | 0.0520" | 1.3208 mm |
| #56 | 0.0465" | 1.1811 mm |
| #57 | 0.0430" | 1.0922 mm |
| #58 | 0.0420" | 1.0668 mm |
| #59 | 0.0410" | 1.0414 mm |
| #60 | 0.0400" | 1.0160 mm |
| #61 | 0.0390" | 0.9906 mm |
| #62 | 0.0380" | 0.9652 mm |
| #63 | 0.0370" | 0.9398 mm |
| #64 | 0.0360" | 0.9144 mm |
| #65 | 0.0350" | 0.8890 mm |
| #66 | 0.0330" | 0.8382 mm |
| #67 | 0.0320" | 0.8128 mm |
| #68 | 0.0310" | 0.7874 mm |
| #69 | 0.0292" | 0.7417 mm |
| #70 | 0.0280" | 0.7112 mm |
| #71 | 0.0260" | 0.6604 mm |
| #72 | 0.0250" | 0.6350 mm |
| #73 | 0.0240" | 0.6096 mm |
| #74 | 0.0225" | 0.5715 mm |
| #75 | 0.0210" | 0.5334 mm |
| #76 | 0.0200" | 0.5080 mm |
| #77 | 0.0180" | 0.4572 mm |
| #78 | 0.0160" | 0.4064 mm |
| #79 | 0.0145" | 0.3683 mm |
| #80 | 0.0135" | 0.3429 mm |
Why the Numbering Runs in Reverse
The number drill system dates back to 19th-century wire and sheet metal gauge numbering, where a higher gauge number meant a thinner (smaller) wire. Drill makers borrowed the same convention: a higher number means a smaller bit. #1 (0.228") is nearly as large as fractional 15/64" (0.2344"), while #80 (0.0135") is a fine pilot-hole size well under 1/64" (0.0156").
Number Drills and Tap Drill Charts
Most small machine-screw tap drills specify a number size rather than a fraction, because the correct pilot hole diameter for cutting clean internal threads usually falls between two fractional sizes. See the tap and clearance drill chart for the full thread-to-drill pairing, or the main drill size chart for the fractional and letter systems.
Frequently Asked Questions
Related Tools
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