Drill Bit Sizes Conversion Chart: Fractional, Number, Letter to MetricFraction, gauge, and letter drill equivalents in inches and mm
This drill bit size chart converts fractional inch, number gauge, and letter drill sizes into decimal inches and millimeters. It is built for machinists, maintenance teams, and procurement engineers who need a fast way to compare drill sizes for CNC setup, tap drill planning, and replacement tooling.
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)β | 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 |
Number & Letter Drill Sizes
Number Gauge (#80β#1)
Number | Decimal (in)β | 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 (AβZ)
Letter | Decimal (in)β | 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 |
How to read the drill bit conversion chart
- Choose fractional, number, or letter drill sizes.
- Search by size, decimal inch, or metric equivalent.
- Sort the table when you need the closest larger or smaller drill.
- Export CSV for purchasing or shop-floor setup sheets.
Common fractional drill sizes in mm
1/8 inch is 3.175 mm, 13/64 inch is 5.159 mm, and 1/2 inch is exactly 12.7 mm. Use the exact inch-to-mm value before choosing the nearest available drill.
Drill Bit Size FAQ
What is a #7 drill bit in mm?
A #7 drill bit is approximately 5.105 mm in diameter. Always confirm whether the job needs the closest available drill or a specified tap drill size.
What is 13/64 inch drill bit in mm?
13/64 inch equals approximately 5.159 mm. Use the decimal value when comparing it to number drills or metric drill inventory.
What is a 1/2 inch drill bit in mm?
A 1/2 inch drill bit is exactly 12.7 mm because 1 inch equals exactly 25.4 mm.
Are number drill sizes the same as metric drill sizes?
No. Number drills are an imperial gauge series. The metric value is a diameter equivalent, not a metric standard drill designation.
Should I choose the nearest metric drill bit?
Not automatically. For clearance holes, close equivalents may work; for tapping or precision fits, use the specified tap drill recommendation or engineering requirement.
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