# Drill size chart: number #1–#80, letter A–Z, fractional 1/64–1 in and metric drills in decimal inches and mm (ASME B94.11M)

> What is the decimal size of a #7, #21, letter F, 'Q' or 'R' drill, and the inch / mm equivalent of fractional and metric drill sizes?

- Category: Hardware › Cutting tools
- Kind: Standard part
- Basis: Starrett's decimal-equivalent bulletin for the number, letter and fractional drills (printed in inches), with spot checks against three other charts; mm columns are computed here (inches × 25.4); numbers only
- Page: https://xemstudio.com/objects/drill-size-index-number-letter-fraction/ · JSON: https://xemstudio.com/api/geometry?object=drill-size-index-number-letter-fraction · Plain text: https://xemstudio.com/objects/drill-size-index-number-letter-fraction/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
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**Exact dimensions.** True size, with no tolerance added.

## Notes

- Drill sizes come in four series. Number drills #1 to #80 (#1 = 0.2280 in is the largest, #80 = 0.0135 in the smallest; CNCCookbook notes ASME B94.11M numbers run to #97 but sizes past #80 are seldom seen), letter drills A to Z (A = 0.2340 in to Z = 0.4130 in), fractional drills from 1/64 in in 1/64 in steps, and metric drills. The decimal inch values for the number, letter and fractional drills are the Starrett table as printed; the mm column is that inch value × 25.4 rounded to 0.001 mm (the fractional mm are the exact fraction × 25.4). The metric rows are the standard mm sizes with the inch value computed as mm ÷ 25.4.
- Cross-checks: Newman Tools lists #1 = 0.2280, #40 = 0.0980, #80 = 0.0135, A = 0.234, E = 0.250, Z = 0.413; Xometry lists #8 = 0.199, A = 0.234 and 3.20 mm = 0.126 in; AIMS Industrial lists #80 = 0.343 mm, #1 = 5.791 mm, A = 5.944 mm and Z = 10.490 mm. All agree with the table here. The metric block is a short list of whole and half millimetres for convenience, not every metric drill size.
- Use: a drill is the size of the hole it cuts only approximately. Real holes run a little over; the clearance and tap-drill tables on thread-reference-tap-drills-clearance give the drill chosen for a thread or a screw. This page is the size lookup, not a hole-fit recommendation. Not here: drill point angle, flute length series (jobber, stub, screw-machine), taps, reamers and fractional drills above 1 in.
- No files: a drill is not a mating geometry on its own and a plate of holes at drill sizes would be a stand-in. The hole-size gauges for specific fasteners (rivet nuts, cable glands, PEM nuts) are on their own pages.

## Sizes

| series | size | decimal (in) | mm (computed) |
|---|---|---|---|
| number | #1 | 0.2280 | 5.791 |
| number | #2 | 0.2210 | 5.613 |
| number | #3 | 0.2130 | 5.410 |
| number | #4 | 0.2090 | 5.309 |
| number | #5 | 0.2055 | 5.220 |
| number | #6 | 0.2040 | 5.182 |
| number | #7 | 0.2010 | 5.105 |
| number | #8 | 0.1990 | 5.055 |
| number | #9 | 0.1960 | 4.978 |
| number | #10 | 0.1935 | 4.915 |
| number | #11 | 0.1910 | 4.851 |
| number | #12 | 0.1890 | 4.801 |
| number | #13 | 0.1850 | 4.699 |
| number | #14 | 0.1820 | 4.623 |
| number | #15 | 0.1800 | 4.572 |
| number | #16 | 0.1770 | 4.496 |
| number | #17 | 0.1730 | 4.394 |
| number | #18 | 0.1695 | 4.305 |
| number | #19 | 0.1660 | 4.216 |
| number | #20 | 0.1610 | 4.089 |
| number | #21 | 0.1590 | 4.039 |
| number | #22 | 0.1570 | 3.988 |
| number | #23 | 0.1540 | 3.912 |
| number | #24 | 0.1520 | 3.861 |
| number | #25 | 0.1495 | 3.797 |
| number | #26 | 0.1470 | 3.734 |
| number | #27 | 0.1440 | 3.658 |
| number | #28 | 0.1405 | 3.569 |
| number | #29 | 0.1360 | 3.454 |
| number | #30 | 0.1285 | 3.264 |
| number | #31 | 0.1200 | 3.048 |
| number | #32 | 0.1160 | 2.946 |
| number | #33 | 0.1130 | 2.870 |
| number | #34 | 0.1110 | 2.819 |
| number | #35 | 0.1100 | 2.794 |
| number | #36 | 0.1065 | 2.705 |
| number | #37 | 0.1040 | 2.642 |
| number | #38 | 0.1015 | 2.578 |
| number | #39 | 0.0995 | 2.527 |
| number | #40 | 0.0980 | 2.489 |
| number | #41 | 0.0960 | 2.438 |
| number | #42 | 0.0935 | 2.375 |
| number | #43 | 0.0890 | 2.261 |
| number | #44 | 0.0860 | 2.184 |
| number | #45 | 0.0820 | 2.083 |
| number | #46 | 0.0810 | 2.057 |
| number | #47 | 0.0785 | 1.994 |
| number | #48 | 0.0760 | 1.930 |
| number | #49 | 0.0730 | 1.854 |
| number | #50 | 0.0700 | 1.778 |
| number | #51 | 0.0670 | 1.702 |
| number | #52 | 0.0635 | 1.613 |
| number | #53 | 0.0595 | 1.511 |
| number | #54 | 0.0550 | 1.397 |
| number | #55 | 0.0520 | 1.321 |
| number | #56 | 0.0465 | 1.181 |
| number | #57 | 0.0430 | 1.092 |
| number | #58 | 0.0420 | 1.067 |
| number | #59 | 0.0410 | 1.041 |
| number | #60 | 0.0400 | 1.016 |
| number | #61 | 0.0390 | 0.991 |
| number | #62 | 0.0380 | 0.965 |
| number | #63 | 0.0370 | 0.940 |
| number | #64 | 0.0360 | 0.914 |
| number | #65 | 0.0350 | 0.889 |
| number | #66 | 0.0330 | 0.838 |
| number | #67 | 0.0320 | 0.813 |
| number | #68 | 0.0310 | 0.787 |
| number | #69 | 0.0292 | 0.742 |
| number | #70 | 0.0280 | 0.711 |
| number | #71 | 0.0260 | 0.660 |
| number | #72 | 0.0250 | 0.635 |
| number | #73 | 0.0240 | 0.610 |
| number | #74 | 0.0225 | 0.571 |
| number | #75 | 0.0210 | 0.533 |
| number | #76 | 0.0200 | 0.508 |
| number | #77 | 0.0180 | 0.457 |
| number | #78 | 0.0160 | 0.406 |
| number | #79 | 0.0145 | 0.368 |
| number | #80 | 0.0135 | 0.343 |
| letter | A | 0.2340 | 5.944 |
| letter | 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 | G | 0.2610 | 6.629 |
| letter | H | 0.2660 | 6.756 |
| letter | I | 0.2720 | 6.909 |
| letter | J | 0.2770 | 7.036 |
| letter | K | 0.2810 | 7.137 |
| letter | L | 0.2900 | 7.366 |
| letter | M | 0.2950 | 7.493 |
| letter | N | 0.3020 | 7.671 |
| letter | O | 0.3160 | 8.026 |
| letter | P | 0.3230 | 8.204 |
| letter | Q | 0.3320 | 8.433 |
| letter | R | 0.3390 | 8.611 |
| letter | S | 0.3480 | 8.839 |
| letter | T | 0.3580 | 9.093 |
| letter | U | 0.3680 | 9.347 |
| letter | V | 0.3770 | 9.576 |
| letter | W | 0.3860 | 9.804 |
| letter | X | 0.3970 | 10.084 |
| letter | Y | 0.4040 | 10.262 |
| letter | Z | 0.4130 | 10.490 |
| fractional | 1/64 in | 0.0156 | 0.397 |
| fractional | 1/32 in | 0.0312 | 0.794 |
| fractional | 3/64 in | 0.0469 | 1.191 |
| fractional | 1/16 in | 0.0625 | 1.587 |
| fractional | 5/64 in | 0.0781 | 1.984 |
| fractional | 3/32 in | 0.0938 | 2.381 |
| fractional | 7/64 in | 0.1094 | 2.778 |
| fractional | 1/8 in | 0.1250 | 3.175 |
| fractional | 9/64 in | 0.1406 | 3.572 |
| fractional | 5/32 in | 0.1562 | 3.969 |
| fractional | 11/64 in | 0.1719 | 4.366 |
| fractional | 3/16 in | 0.1875 | 4.762 |
| fractional | 13/64 in | 0.2031 | 5.159 |
| fractional | 7/32 in | 0.2188 | 5.556 |
| fractional | 15/64 in | 0.2344 | 5.953 |
| fractional | 1/4 in | 0.2500 | 6.350 |
| fractional | 17/64 in | 0.2656 | 6.747 |
| fractional | 9/32 in | 0.2812 | 7.144 |
| fractional | 19/64 in | 0.2969 | 7.541 |
| fractional | 5/16 in | 0.3125 | 7.938 |
| fractional | 21/64 in | 0.3281 | 8.334 |
| fractional | 11/32 in | 0.3438 | 8.731 |
| fractional | 23/64 in | 0.3594 | 9.128 |
| fractional | 3/8 in | 0.3750 | 9.525 |
| fractional | 25/64 in | 0.3906 | 9.922 |
| fractional | 13/32 in | 0.4062 | 10.319 |
| fractional | 27/64 in | 0.4219 | 10.716 |
| fractional | 7/16 in | 0.4375 | 11.112 |
| fractional | 29/64 in | 0.4531 | 11.509 |
| fractional | 15/32 in | 0.4688 | 11.906 |
| fractional | 31/64 in | 0.4844 | 12.303 |
| fractional | 1/2 in | 0.5000 | 12.700 |
| fractional | 33/64 in | 0.5156 | 13.097 |
| fractional | 17/32 in | 0.5312 | 13.494 |
| fractional | 35/64 in | 0.5469 | 13.891 |
| fractional | 9/16 in | 0.5625 | 14.287 |
| fractional | 37/64 in | 0.5781 | 14.684 |
| fractional | 19/32 in | 0.5938 | 15.081 |
| fractional | 39/64 in | 0.6094 | 15.478 |
| fractional | 5/8 in | 0.6250 | 15.875 |
| fractional | 41/64 in | 0.6406 | 16.272 |
| fractional | 21/32 in | 0.6562 | 16.669 |
| fractional | 43/64 in | 0.6719 | 17.066 |
| fractional | 11/16 in | 0.6875 | 17.462 |
| fractional | 45/64 in | 0.7031 | 17.859 |
| fractional | 23/32 in | 0.7188 | 18.256 |
| fractional | 47/64 in | 0.7344 | 18.653 |
| fractional | 3/4 in | 0.7500 | 19.050 |
| fractional | 49/64 in | 0.7656 | 19.447 |
| fractional | 25/32 in | 0.7812 | 19.844 |
| fractional | 51/64 in | 0.7969 | 20.241 |
| fractional | 13/16 in | 0.8125 | 20.637 |
| fractional | 53/64 in | 0.8281 | 21.034 |
| fractional | 27/32 in | 0.8438 | 21.431 |
| fractional | 55/64 in | 0.8594 | 21.828 |
| fractional | 7/8 in | 0.8750 | 22.225 |
| fractional | 57/64 in | 0.8906 | 22.622 |
| fractional | 29/32 in | 0.9062 | 23.019 |
| fractional | 59/64 in | 0.9219 | 23.416 |
| fractional | 15/16 in | 0.9375 | 23.812 |
| fractional | 61/64 in | 0.9531 | 24.209 |
| fractional | 31/32 in | 0.9688 | 24.606 |
| fractional | 63/64 in | 0.9844 | 25.003 |
| fractional | 1 in | 1.0000 | 25.400 |
| metric | 0.5 mm | 0.0197 | 0.5 |
| metric | 1 mm | 0.0394 | 1 |
| metric | 1.5 mm | 0.0591 | 1.5 |
| metric | 2 mm | 0.0787 | 2 |
| metric | 2.5 mm | 0.0984 | 2.5 |
| metric | 3 mm | 0.1181 | 3 |
| metric | 3.5 mm | 0.1378 | 3.5 |
| metric | 4 mm | 0.1575 | 4 |
| metric | 4.5 mm | 0.1772 | 4.5 |
| metric | 5 mm | 0.1969 | 5 |
| metric | 5.5 mm | 0.2165 | 5.5 |
| metric | 6 mm | 0.2362 | 6 |
| metric | 6.5 mm | 0.2559 | 6.5 |
| metric | 7 mm | 0.2756 | 7 |
| metric | 7.5 mm | 0.2953 | 7.5 |
| metric | 8 mm | 0.3150 | 8 |
| metric | 8.5 mm | 0.3346 | 8.5 |
| metric | 9 mm | 0.3543 | 9 |
| metric | 9.5 mm | 0.3740 | 9.5 |
| metric | 10 mm | 0.3937 | 10 |
| metric | 10.5 mm | 0.4134 | 10.5 |
| metric | 11 mm | 0.4331 | 11 |
| metric | 11.5 mm | 0.4528 | 11.5 |
| metric | 12 mm | 0.4724 | 12 |
| metric | 12.5 mm | 0.4921 | 12.5 |
| metric | 13 mm | 0.5118 | 13 |
| metric | 14 mm | 0.5512 | 14 |
| metric | 15 mm | 0.5906 | 15 |
| metric | 16 mm | 0.6299 | 16 |
| metric | 17 mm | 0.6693 | 17 |
| metric | 18 mm | 0.7087 | 18 |
| metric | 19 mm | 0.7480 | 19 |
| metric | 20 mm | 0.7874 | 20 |
| metric | 22 mm | 0.8661 | 22 |
| metric | 25 mm | 0.9843 | 25 |

## Where the files are

- Starrett (bulletin hosted by FIU): [Decimal and tap chart: number drills 80-1, letter drills A-Z, fractional drills 1/64 to 1-1/2 in, metric tap drills](https://web.eng.fiu.edu/zicarell/EIN3390L%20DATA/Technical%20Info/Decimal%20and%20Tap%20chart_Starrett.pdf) — web — Publisher's page; dimensions are facts
- Newman Tools: [Decimal equivalents: fractional, number, letter and metric drill sizes (spot-check of #1, #40, #80, A, E, Z)](https://newmantools.com/decinch.htm) — web — Publisher's page; dimensions are facts
- Xometry: [Standard drill sizes chart (spot-check of #8, A, 1/8, 5/16, 3.20 mm)](https://community.xometry.com/kb/articles/723-standard-drill-sizes) — web — Publisher's page; dimensions are facts
- AIMS Industrial: [Drill bit metric / imperial size chart (spot-check of #80 0.343 mm, #1 5.791 mm, A 5.944 mm, Z 10.490 mm)](https://aimsindustrial.com.au/blogs/product-guides/blog-drill-bit-metric-imperial-size-chart) — web — Publisher's page; dimensions are facts
- CNCCookbook: [Drill chart bit sizes: number, letter, fractional and metric series, ASME B94.11M number range](https://www.cnccookbook.com/drill-chart-bit-sizes-decimal-number-letter-metric) — web — Publisher's page; dimensions are facts

## Questions

**What is the decimal size of a #7 drill?**

0.2010 in (5.105 mm computed).

**What is the size of a letter Q drill?**

0.3320 in (8.433 mm computed).

**What is a #1 drill in mm?**

0.2280 in = 5.791 mm.

**What is the smallest number drill?**

#80, 0.0135 in (0.343 mm); #1 is the largest number drill at 0.2280 in.

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