The converter ships the complete number and letter lookup used by the calculation engine. Individual dimensions were cross-checked against the cited Travers technical chart.
Complete number and letter drill lookup
The metric column is an exact unit conversion rounded to three decimals for display.
| Designation | Series | Diameter (in) | Diameter (mm) |
|---|---|---|---|
| #1 | number | .2280 | 5.791 |
| #2 | number | .2210 | 5.613 |
| #3 | number | .2130 | 5.410 |
| #4 | number | .2090 | 5.309 |
| #5 | number | .2055 | 5.220 |
| #6 | number | .2040 | 5.182 |
| #7 | number | .2010 | 5.105 |
| #8 | number | .1990 | 5.055 |
| #9 | number | .1960 | 4.978 |
| #10 | number | .1935 | 4.915 |
| #11 | number | .1910 | 4.851 |
| #12 | number | .1890 | 4.801 |
| #13 | number | .1850 | 4.699 |
| #14 | number | .1820 | 4.623 |
| #15 | number | .1800 | 4.572 |
| #16 | number | .1770 | 4.496 |
| #17 | number | .1730 | 4.394 |
| #18 | number | .1695 | 4.305 |
| #19 | number | .1660 | 4.216 |
| #20 | number | .1610 | 4.089 |
| #21 | number | .1590 | 4.039 |
| #22 | number | .1570 | 3.988 |
| #23 | number | .1540 | 3.912 |
| #24 | number | .1520 | 3.861 |
| #25 | number | .1495 | 3.797 |
| #26 | number | .1470 | 3.734 |
| #27 | number | .1440 | 3.658 |
| #28 | number | .1405 | 3.569 |
| #29 | number | .1360 | 3.454 |
| #30 | number | .1285 | 3.264 |
| #31 | number | .1200 | 3.048 |
| #32 | number | .1160 | 2.946 |
| #33 | number | .1130 | 2.870 |
| #34 | number | .1110 | 2.819 |
| #35 | number | .1100 | 2.794 |
| #36 | number | .1065 | 2.705 |
| #37 | number | .1040 | 2.642 |
| #38 | number | .1015 | 2.578 |
| #39 | number | .0995 | 2.527 |
| #40 | number | .0980 | 2.489 |
| #41 | number | .0960 | 2.438 |
| #42 | number | .0935 | 2.375 |
| #43 | number | .0890 | 2.261 |
| #44 | number | .0860 | 2.184 |
| #45 | number | .0820 | 2.083 |
| #46 | number | .0810 | 2.057 |
| #47 | number | .0785 | 1.994 |
| #48 | number | .0760 | 1.930 |
| #49 | number | .0730 | 1.854 |
| #50 | number | .0700 | 1.778 |
| #51 | number | .0670 | 1.702 |
| #52 | number | .0635 | 1.613 |
| #53 | number | .0595 | 1.511 |
| #54 | number | .0550 | 1.397 |
| #55 | number | .0520 | 1.321 |
| #56 | number | .0465 | 1.181 |
| #57 | number | .0430 | 1.092 |
| #58 | number | .0420 | 1.067 |
| #59 | number | .0410 | 1.041 |
| #60 | number | .0400 | 1.016 |
| #61 | number | .0390 | 0.991 |
| #62 | number | .0380 | 0.965 |
| #63 | number | .0370 | 0.940 |
| #64 | number | .0360 | 0.914 |
| #65 | number | .0350 | 0.889 |
| #66 | number | .0330 | 0.838 |
| #67 | number | .0320 | 0.813 |
| #68 | number | .0310 | 0.787 |
| #69 | number | .0292 | 0.742 |
| #70 | number | .0280 | 0.711 |
| #71 | number | .0260 | 0.660 |
| #72 | number | .0250 | 0.635 |
| #73 | number | .0240 | 0.610 |
| #74 | number | .0225 | 0.572 |
| #75 | number | .0210 | 0.533 |
| #76 | number | .0200 | 0.508 |
| #77 | number | .0180 | 0.457 |
| #78 | number | .0160 | 0.406 |
| #79 | number | .0145 | 0.368 |
| #80 | number | .0135 | 0.343 |
| A | letter | .2340 | 5.944 |
| B | letter | .2380 | 6.045 |
| C | letter | .2420 | 6.147 |
| D | letter | .2460 | 6.248 |
| E | letter | .2500 | 6.350 |
| F | letter | .2570 | 6.528 |
| G | letter | .2610 | 6.629 |
| H | letter | .2660 | 6.756 |
| I | letter | .2720 | 6.909 |
| J | letter | .2770 | 7.036 |
| K | letter | .2810 | 7.137 |
| L | letter | .2900 | 7.366 |
| M | letter | .2950 | 7.493 |
| N | letter | .3020 | 7.671 |
| O | letter | .3160 | 8.026 |
| P | letter | .3230 | 8.204 |
| Q | letter | .3320 | 8.433 |
| R | letter | .3390 | 8.611 |
| S | letter | .3480 | 8.839 |
| T | letter | .3580 | 9.093 |
| U | letter | .3680 | 9.347 |
| V | letter | .3770 | 9.576 |
| W | letter | .3860 | 9.804 |
| X | letter | .3970 | 10.084 |
| Y | letter | .4040 | 10.262 |
| Z | letter | .4130 | 10.490 |
Why these systems exist
Number and letter drills fill diameter gaps between common fractional sizes. They are especially common in tap-drill recommendations where a small diameter change affects engagement and tapping torque.
Reading the sequence
#80 is the smallest number drill in the usual series and #1 is the largest. After the number range, letter A begins at 0.2340 inch and the sequence continues to Z at 0.4130 inch.
Important limitation
The lookup is nominal. Verify the actual tool and produced hole when tolerance matters.
The lookup is nominal. Verify the actual tool and produced hole when tolerance matters.
Technical references
- Decimal Equivalent & Drill Size Chart — Travers Tool Co.. Accessed 2026-11-09.
- SI Units – Length — National Institute of Standards and Technology. Accessed 2026-11-09.
Standards references identify scope and terminology; protected dimensional tables are not reproduced.