Drill Bit Sizes Conversion ChartFractional, Number, Letter to Metric
Shop-floor reference for drill diameters. Fractional inch sizes converted to decimal inch and millimeters with the exact 25.4 factor. Complete Number gauge (#80–#1) and Letter sizes (A–Z) tables with search, sort, print and CSV export.
Precision Equivalents
Decimal inch and metric mm values based on the exact 1" = 25.4 mm standard.
Print-Optimized
Clean table layout designed for A4/Letter printing and quick reference.
Manufacturing Focus
Ideal for tap drill selection, clearance holes, and fixture design.
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Fractional Drill Bit Sizes (1/64" to 1")
Fraction | Decimal (in)↑ | Metric (mm) |
|---|---|---|
| 1/64" | 0.01563 | 0.397 |
| 1/32" | 0.03125 | 0.794 |
| 3/64" | 0.04688 | 1.191 |
| 1/16" | 0.06250 | 1.587 |
| 5/64" | 0.07813 | 1.984 |
| 3/32" | 0.09375 | 2.381 |
| 7/64" | 0.10938 | 2.778 |
| 1/8" | 0.12500 | 3.175 |
| 9/64" | 0.14063 | 3.572 |
| 5/32" | 0.15625 | 3.969 |
| 11/64" | 0.17188 | 4.366 |
| 3/16" | 0.18750 | 4.762 |
| 13/64" | 0.20313 | 5.159 |
| 7/32" | 0.21875 | 5.556 |
| 15/64" | 0.23438 | 5.953 |
| 1/4" | 0.25000 | 6.350 |
| 17/64" | 0.26563 | 6.747 |
| 9/32" | 0.28125 | 7.144 |
| 19/64" | 0.29688 | 7.541 |
| 5/16" | 0.31250 | 7.938 |
| 21/64" | 0.32813 | 8.334 |
| 11/32" | 0.34375 | 8.731 |
| 23/64" | 0.35938 | 9.128 |
| 3/8" | 0.37500 | 9.525 |
| 25/64" | 0.39063 | 9.922 |
| 13/32" | 0.40625 | 10.319 |
| 27/64" | 0.42188 | 10.716 |
| 7/16" | 0.43750 | 11.112 |
| 29/64" | 0.45313 | 11.509 |
| 15/32" | 0.46875 | 11.906 |
| 31/64" | 0.48438 | 12.303 |
| 1/2" | 0.50000 | 12.700 |
| 33/64" | 0.51563 | 13.097 |
| 17/32" | 0.53125 | 13.494 |
| 35/64" | 0.54688 | 13.891 |
| 9/16" | 0.56250 | 14.287 |
| 37/64" | 0.57813 | 14.684 |
| 19/32" | 0.59375 | 15.081 |
| 39/64" | 0.60938 | 15.478 |
| 5/8" | 0.62500 | 15.875 |
| 41/64" | 0.64063 | 16.272 |
| 21/32" | 0.65625 | 16.669 |
| 43/64" | 0.67188 | 17.066 |
| 11/16" | 0.68750 | 17.462 |
| 45/64" | 0.70313 | 17.859 |
| 23/32" | 0.71875 | 18.256 |
| 47/64" | 0.73438 | 18.653 |
| 3/4" | 0.75000 | 19.050 |
| 49/64" | 0.76563 | 19.447 |
| 25/32" | 0.78125 | 19.844 |
| 51/64" | 0.79688 | 20.241 |
| 13/16" | 0.81250 | 20.637 |
| 53/64" | 0.82813 | 21.034 |
| 27/32" | 0.84375 | 21.431 |
| 55/64" | 0.85938 | 21.828 |
| 7/8" | 0.87500 | 22.225 |
| 57/64" | 0.89063 | 22.622 |
| 29/32" | 0.90625 | 23.019 |
| 59/64" | 0.92188 | 23.416 |
| 15/16" | 0.93750 | 23.813 |
| 61/64" | 0.95313 | 24.209 |
| 31/32" | 0.96875 | 24.606 |
| 63/64" | 0.98438 | 25.003 |
| 1/1" | 1.00000 | 25.400 |
Formula:1" = 25.4 mm
Precision:Inch × 25.4 (exact)
Number & Letter Drill Sizes
Number Gauge (#80–#1)
Number | Decimal (in)↑ | Metric (mm) |
|---|---|---|
| #80 | 0.0135 | 0.34 |
| #79 | 0.0145 | 0.37 |
| #78 | 0.0160 | 0.41 |
| #77 | 0.0180 | 0.46 |
| #76 | 0.0200 | 0.51 |
| #75 | 0.0210 | 0.53 |
| #74 | 0.0225 | 0.57 |
| #73 | 0.0240 | 0.61 |
| #72 | 0.0250 | 0.64 |
| #71 | 0.0260 | 0.66 |
| #70 | 0.0280 | 0.71 |
| #69 | 0.0290 | 0.74 |
| #68 | 0.0310 | 0.79 |
| #67 | 0.0320 | 0.81 |
| #66 | 0.0330 | 0.84 |
| #65 | 0.0350 | 0.89 |
| #64 | 0.0360 | 0.91 |
| #63 | 0.0370 | 0.94 |
| #62 | 0.0380 | 0.97 |
| #61 | 0.0390 | 0.99 |
| #60 | 0.0400 | 1.02 |
| #59 | 0.0410 | 1.04 |
| #58 | 0.0420 | 1.07 |
| #57 | 0.0430 | 1.09 |
| #56 | 0.0465 | 1.18 |
| #55 | 0.0520 | 1.32 |
| #54 | 0.0550 | 1.40 |
| #53 | 0.0595 | 1.51 |
| #52 | 0.0635 | 1.61 |
| #51 | 0.0670 | 1.70 |
| #50 | 0.0700 | 1.78 |
| #49 | 0.0730 | 1.85 |
| #48 | 0.0760 | 1.93 |
| #47 | 0.0785 | 1.99 |
| #46 | 0.0810 | 2.06 |
| #45 | 0.0820 | 2.08 |
| #44 | 0.0860 | 2.18 |
| #43 | 0.0890 | 2.26 |
| #42 | 0.0935 | 2.37 |
| #41 | 0.0960 | 2.44 |
| #40 | 0.0980 | 2.49 |
| #39 | 0.0995 | 2.53 |
| #38 | 0.1015 | 2.58 |
| #37 | 0.1040 | 2.64 |
| #36 | 0.1065 | 2.71 |
| #35 | 0.1100 | 2.79 |
| #34 | 0.1110 | 2.82 |
| #33 | 0.1130 | 2.87 |
| #32 | 0.1160 | 2.95 |
| #31 | 0.1200 | 3.05 |
| #30 | 0.1285 | 3.26 |
| #29 | 0.1360 | 3.45 |
| #28 | 0.1400 | 3.56 |
| #27 | 0.1440 | 3.66 |
| #26 | 0.1470 | 3.73 |
| #25 | 0.1500 | 3.81 |
| #24 | 0.1520 | 3.86 |
| #23 | 0.1540 | 3.91 |
| #22 | 0.1570 | 3.99 |
| #21 | 0.1590 | 4.04 |
| #20 | 0.1610 | 4.09 |
| #19 | 0.1660 | 4.22 |
| #18 | 0.1700 | 4.32 |
| #17 | 0.1730 | 4.39 |
| #16 | 0.1770 | 4.50 |
| #15 | 0.1800 | 4.57 |
| #14 | 0.1820 | 4.62 |
| #13 | 0.1850 | 4.70 |
| #12 | 0.1890 | 4.80 |
| #11 | 0.1910 | 4.85 |
| #10 | 0.1930 | 4.90 |
| #9 | 0.1960 | 4.98 |
| #8 | 0.1990 | 5.05 |
| #7 | 0.2010 | 5.11 |
| #6 | 0.2040 | 5.18 |
| #5 | 0.2050 | 5.21 |
| #4 | 0.2090 | 5.31 |
| #3 | 0.2130 | 5.41 |
| #2 | 0.2210 | 5.61 |
| #1 | 0.2280 | 5.79 |
Letter Series (A–Z)
Letter | Decimal (in)↑ | Metric (mm) |
|---|---|---|
| A | 0.234 | 5.94 |
| B | 0.238 | 6.05 |
| C | 0.242 | 6.15 |
| D | 0.246 | 6.25 |
| E | 0.250 | 6.35 |
| F | 0.257 | 6.53 |
| G | 0.261 | 6.63 |
| H | 0.266 | 6.76 |
| I | 0.272 | 6.91 |
| J | 0.277 | 7.04 |
| K | 0.281 | 7.14 |
| L | 0.290 | 7.37 |
| M | 0.295 | 7.49 |
| N | 0.302 | 7.67 |
| O | 0.316 | 8.03 |
| P | 0.323 | 8.20 |
| Q | 0.332 | 8.43 |
| R | 0.339 | 8.61 |
| S | 0.348 | 8.84 |
| T | 0.358 | 9.09 |
| U | 0.368 | 9.35 |
| V | 0.377 | 9.58 |
| W | 0.386 | 9.80 |
| X | 0.397 | 10.08 |
| Y | 0.404 | 10.26 |
| Z | 0.413 | 10.49 |
Range:#80–#1, A–Z
Use Cases:Tap drills, clearance holes, pilot holes
Use With Tap Drill Recommendations
Select tap drills using the 75% thread engagement rule. Cross-link from the Fastener Matcher to the exact drill size row in this chart.