Fractional drill chart
Fractional-inch drill sizes from 1/64 to 1 inch with their decimal and millimeter equivalents. Fractional drills are the everyday set, jumping in 1/64 inch steps through the small sizes.
Fractional drill sizes
| Fraction | Decimal (in) | mm |
|---|---|---|
| 1/64 | 0.0156 | 0.396 |
| 1/32 | 0.0313 | 0.795 |
| 3/64 | 0.0469 | 1.191 |
| 1/16 | 0.0625 | 1.587 |
| 5/64 | 0.0781 | 1.984 |
| 3/32 | 0.0938 | 2.383 |
| 7/64 | 0.1094 | 2.779 |
| 1/8 | 0.1250 | 3.175 |
| 9/64 | 0.1406 | 3.571 |
| 5/32 | 0.1563 | 3.970 |
| 11/64 | 0.1719 | 4.366 |
| 3/16 | 0.1875 | 4.762 |
| 13/64 | 0.2031 | 5.159 |
| 7/32 | 0.2188 | 5.558 |
| 15/64 | 0.2344 | 5.954 |
| 1/4 | 0.2500 | 6.350 |
| 17/64 | 0.2656 | 6.746 |
| 9/32 | 0.2813 | 7.145 |
| 19/64 | 0.2969 | 7.541 |
| 5/16 | 0.3125 | 7.938 |
| 21/64 | 0.3281 | 8.334 |
| 11/32 | 0.3438 | 8.733 |
| 23/64 | 0.3594 | 9.129 |
| 3/8 | 0.3750 | 9.525 |
| 25/64 | 0.3906 | 9.921 |
| 13/32 | 0.4063 | 10.320 |
| 27/64 | 0.4219 | 10.716 |
| 7/16 | 0.4375 | 11.112 |
| 29/64 | 0.4531 | 11.509 |
| 15/32 | 0.4688 | 11.908 |
| 31/64 | 0.4844 | 12.304 |
| 1/2 | 0.5000 | 12.700 |
| 9/16 | 0.5625 | 14.287 |
| 5/8 | 0.6250 | 15.875 |
| 11/16 | 0.6875 | 17.462 |
| 3/4 | 0.7500 | 19.050 |
| 13/16 | 0.8125 | 20.637 |
| 7/8 | 0.8750 | 22.225 |
| 15/16 | 0.9375 | 23.813 |
| 1 | 1.0000 | 25.400 |
Fractional drills step in sixty-fourths of an inch and are the most common bits in a shop. For holes between fractional sizes, the number (#1 to #80) and letter (A to Z) drill series fill the gaps with finer increments, which is why all three series are used together for precise tap and clearance holes.
Need a tap or clearance hole size?
See the full Drill Size Chart, or the Tap Drill Calculator for threaded holes.
How the drill series fit together
A complete drill index runs three overlapping series: fractional in 1/64 inch steps, number drills #1 (0.228 in) down to #80 (0.0135 in), and letter drills A (0.234 in) to Z (0.413 in). Together they give a fine ladder of sizes so almost any required diameter can be matched within a few thousandths of an inch.
Reading decimal equivalents
Each fraction has an exact decimal value, found by dividing the numerator by the denominator: 1/4 is 0.250 inch, 3/8 is 0.375. Drill charts list these so you can compare across the fractional, number, and letter series, all expressed in decimal inches, and pick the closest available bit.
FAQ
What is 3/8 inch in decimal?
0.375 inch, or 9.525 mm. It is one of the most common fractional drill sizes.
What comes between fractional drill sizes?
The number and letter drill series. They provide finer increments than the 1/64 inch fractional steps, useful for exact tap and clearance holes.
How do I convert a fraction to a drill decimal?
Divide the top number by the bottom: 5/16 is 5 divided by 16, or 0.3125 inch. The chart lists these so you do not have to.