Drill Bit Chart: Inch and Metric Size Equivalents
Look up fractional drill bits from 1/64 to 1 inch, selected numbered sizes and every letter size, with decimal-inch and metric conversions.
Use these tables to compare nominal drill-bit diameters, not to choose a tap drill or screw pilot hole. They cover fractional sizes from 1/64 to 1 inch, selected numbered drills, and all letter sizes from A to Z.
The inch and millimeter columns describe the same bit. A nearby metric size is not necessarily an interchangeable substitute. Values below are rounded to four decimal places where needed; that precision is for conversion, not a promise about the finished hole.
Fractional drill-bit chart: 1/64 to 1 inch
Sizes are listed in increasing diameter, in 1/64-inch steps. Diameter conversions are listed in the CustomPartNet drill-size reference.
| Fractional size (in) | Decimal inches | Millimeters |
|---|---|---|
| 1/64 | 0.0156 | 0.3969 |
| 1/32 | 0.0313 | 0.7938 |
| 3/64 | 0.0469 | 1.1906 |
| 1/16 | 0.0625 | 1.5875 |
| 5/64 | 0.0781 | 1.9844 |
| 3/32 | 0.0938 | 2.3813 |
| 7/64 | 0.1094 | 2.7781 |
| 1/8 | 0.1250 | 3.1750 |
| 9/64 | 0.1406 | 3.5719 |
| 5/32 | 0.1563 | 3.9688 |
| 11/64 | 0.1719 | 4.3656 |
| 3/16 | 0.1875 | 4.7625 |
| 13/64 | 0.2031 | 5.1594 |
| 7/32 | 0.2188 | 5.5563 |
| 15/64 | 0.2344 | 5.9531 |
| 1/4 | 0.2500 | 6.3500 |
| 17/64 | 0.2656 | 6.7469 |
| 9/32 | 0.2813 | 7.1438 |
| 19/64 | 0.2969 | 7.5406 |
| 5/16 | 0.3125 | 7.9375 |
| 21/64 | 0.3281 | 8.3344 |
| 11/32 | 0.3438 | 8.7313 |
| 23/64 | 0.3594 | 9.1281 |
| 3/8 | 0.3750 | 9.5250 |
| 25/64 | 0.3906 | 9.9219 |
| 13/32 | 0.4063 | 10.3188 |
| 27/64 | 0.4219 | 10.7156 |
| 7/16 | 0.4375 | 11.1125 |
| 29/64 | 0.4531 | 11.5094 |
| 15/32 | 0.4688 | 11.9063 |
| 31/64 | 0.4844 | 12.3031 |
| 1/2 | 0.5000 | 12.7000 |
| 33/64 | 0.5156 | 13.0969 |
| 17/32 | 0.5313 | 13.4938 |
| 35/64 | 0.5469 | 13.8906 |
| 9/16 | 0.5625 | 14.2875 |
| 37/64 | 0.5781 | 14.6844 |
| 19/32 | 0.5938 | 15.0813 |
| 39/64 | 0.6094 | 15.4781 |
| 5/8 | 0.6250 | 15.8750 |
| 41/64 | 0.6406 | 16.2719 |
| 21/32 | 0.6563 | 16.6688 |
| 43/64 | 0.6719 | 17.0656 |
| 11/16 | 0.6875 | 17.4625 |
| 45/64 | 0.7031 | 17.8594 |
| 23/32 | 0.7188 | 18.2563 |
| 47/64 | 0.7344 | 18.6531 |
| 3/4 | 0.7500 | 19.0500 |
| 49/64 | 0.7656 | 19.4469 |
| 25/32 | 0.7813 | 19.8438 |
| 51/64 | 0.7969 | 20.2406 |
| 13/16 | 0.8125 | 20.6375 |
| 53/64 | 0.8281 | 21.0344 |
| 27/32 | 0.8438 | 21.4313 |
| 55/64 | 0.8594 | 21.8281 |
| 7/8 | 0.8750 | 22.2250 |
| 57/64 | 0.8906 | 22.6219 |
| 29/32 | 0.9063 | 23.0188 |
| 59/64 | 0.9219 | 23.4156 |
| 15/16 | 0.9375 | 23.8125 |
| 61/64 | 0.9531 | 24.2094 |
| 31/32 | 0.9688 | 24.6063 |
| 63/64 | 0.9844 | 25.0031 |
| 1 | 1.0000 | 25.4000 |
Selected numbered drill sizes
Numbered drills get larger as the number gets smaller. The number is a size designation, not a measurement in inches or millimeters. This is a selected lookup table, not the complete numbered series; the full CustomPartNet chart includes the intervening sizes and smaller drills.
| Number size | Decimal inches | Millimeters |
|---|---|---|
| No. 80 | 0.0135 | 0.3429 |
| No. 70 | 0.0280 | 0.7112 |
| No. 60 | 0.0400 | 1.0160 |
| No. 55 | 0.0520 | 1.3208 |
| No. 50 | 0.0700 | 1.7780 |
| No. 47 | 0.0785 | 1.9939 |
| No. 43 | 0.0890 | 2.2606 |
| No. 40 | 0.0980 | 2.4892 |
| No. 36 | 0.1065 | 2.7051 |
| No. 30 | 0.1285 | 3.2639 |
| No. 29 | 0.1360 | 3.4544 |
| No. 25 | 0.1495 | 3.7973 |
| No. 21 | 0.1590 | 4.0386 |
| No. 16 | 0.1770 | 4.4958 |
| No. 12 | 0.1890 | 4.8006 |
| No. 7 | 0.2010 | 5.1054 |
| No. 3 | 0.2130 | 5.4102 |
| No. 1 | 0.2280 | 5.7912 |
Letter drill-bit chart: A to Z
Letter drills get larger from A to Z, as shown in LittleMachineShop’s letter-drill chart. The millimeter conversions below use the inch diameters multiplied by 25.4.
| Letter size | Decimal inches | Millimeters |
|---|---|---|
| A | 0.2340 | 5.9436 |
| B | 0.2380 | 6.0452 |
| C | 0.2420 | 6.1468 |
| D | 0.2460 | 6.2484 |
| E | 0.2500 | 6.3500 |
| F | 0.2570 | 6.5278 |
| G | 0.2610 | 6.6294 |
| H | 0.2660 | 6.7564 |
| I | 0.2720 | 6.9088 |
| J | 0.2770 | 7.0358 |
| K | 0.2810 | 7.1374 |
| L | 0.2900 | 7.3660 |
| M | 0.2950 | 7.4930 |
| N | 0.3020 | 7.6708 |
| O | 0.3160 | 8.0264 |
| P | 0.3230 | 8.2042 |
| Q | 0.3320 | 8.4328 |
| R | 0.3390 | 8.6106 |
| S | 0.3480 | 8.8392 |
| T | 0.3580 | 9.0932 |
| U | 0.3680 | 9.3472 |
| V | 0.3770 | 9.5758 |
| W | 0.3860 | 9.8044 |
| X | 0.3970 | 10.0838 |
| Y | 0.4040 | 10.2616 |
| Z | 0.4130 | 10.4902 |
Compare sizes without mistaking “close” for “equal”
To convert any size, use:
- Inches to millimeters: multiply by 25.4.
- Millimeters to inches: divide by 25.4.
NIST’s conversion guidance gives the 25.4 conversion factor and advises calculating from the original value rather than an already-rounded conversion. For fractional bits, calculate from the fraction rather than the rounded decimal-inch column above.
For example, 1/4 inch and letter E share the same nominal diameter: 0.2500 inch, or 6.35 mm. A 6 mm bit is smaller; a 6.5 mm bit is larger. Neither is an exact equivalent.
For a proposed substitute, subtract the specified diameter from the alternative diameter in the same units. A positive result means a larger bit; a negative result means a smaller one. Use the specified size when the drawing or hardware instructions do not allow that difference.
Need a tap-drill size instead?
A diameter chart does not tell you which hole to drill before threading. Tap-and-clearance charts distinguish the tap hole from the hole that lets a screw pass through, and list choices by thread and fit.
For thread-specific guidance, use the 1/4-20 cutting-tap drill guide or the M6 tap-drill guide, rather than matching the bit to the thread’s nominal outside diameter.