Machining reference
Drill Bit Size Chart
Fractional drill bit sizes in 64ths, with decimal inch and millimetre equivalents.
- Basis Computed from definitions
- Last checked 2026-08-17
- Sheet portrait
Both unit systems load with the page. The filter searches every column.
| Size | Diameter | Diameter | Diameter | |
|---|---|---|---|---|
| in | mm | |||
| 1/64 | 0.0156 | 0.397 | ||
| 1/32 | 0.0313 | 0.794 | ||
| 3/64 | 0.0469 | 1.191 | ||
| 1/16 | 0.0625 | 1.588 | ||
| 5/64 | 0.0781 | 1.984 | ||
| 3/32 | 0.0938 | 2.381 | ||
| 7/64 | 0.1094 | 2.778 | ||
| 1/8 | 0.1250 | 3.175 | ||
| 9/64 | 0.1406 | 3.572 | ||
| 5/32 | 0.1563 | 3.969 | ||
| 11/64 | 0.1719 | 4.366 | ||
| 3/16 | 0.1875 | 4.762 | ||
| 13/64 | 0.2031 | 5.159 | ||
| 7/32 | 0.2188 | 5.556 | ||
| 15/64 | 0.2344 | 5.953 | ||
| 1/4 | 0.2500 | 6.350 | ||
| 17/64 | 0.2656 | 6.747 | ||
| 9/32 | 0.2813 | 7.144 | ||
| 19/64 | 0.2969 | 7.541 | ||
| 5/16 | 0.3125 | 7.938 | ||
| 21/64 | 0.3281 | 8.334 | ||
| 11/32 | 0.3438 | 8.731 | ||
| 23/64 | 0.3594 | 9.128 | ||
| 3/8 | 0.3750 | 9.525 | ||
| 25/64 | 0.3906 | 9.922 | ||
| 13/32 | 0.4063 | 10.319 | ||
| 27/64 | 0.4219 | 10.716 | ||
| 7/16 | 0.4375 | 11.112 | ||
| 29/64 | 0.4531 | 11.509 | ||
| 15/32 | 0.4688 | 11.906 | ||
| 31/64 | 0.4844 | 12.303 | ||
| 1/2 | 0.5000 | 12.700 | ||
| 33/64 | 0.5156 | 13.097 | ||
| 17/32 | 0.5313 | 13.494 | ||
| 35/64 | 0.5469 | 13.891 | ||
| 9/16 | 0.5625 | 14.288 | ||
| 37/64 | 0.5781 | 14.684 | ||
| 19/32 | 0.5938 | 15.081 | ||
| 39/64 | 0.6094 | 15.478 | ||
| 5/8 | 0.6250 | 15.875 | ||
| 41/64 | 0.6406 | 16.272 | ||
| 21/32 | 0.6563 | 16.669 | ||
| 43/64 | 0.6719 | 17.066 | ||
| 11/16 | 0.6875 | 17.463 | ||
| 45/64 | 0.7031 | 17.859 | ||
| 23/32 | 0.7188 | 18.256 | ||
| 47/64 | 0.7344 | 18.653 | ||
| 3/4 | 0.7500 | 19.050 | ||
| 49/64 | 0.7656 | 19.447 | ||
| 25/32 | 0.7813 | 19.844 | ||
| 51/64 | 0.7969 | 20.241 | ||
| 13/16 | 0.8125 | 20.638 | ||
| 53/64 | 0.8281 | 21.034 | ||
| 27/32 | 0.8438 | 21.431 | ||
| 55/64 | 0.8594 | 21.828 | ||
| 7/8 | 0.8750 | 22.225 | ||
| 57/64 | 0.8906 | 22.622 | ||
| 29/32 | 0.9063 | 23.019 | ||
| 59/64 | 0.9219 | 23.416 | ||
| 15/16 | 0.9375 | 23.813 | ||
| 61/64 | 0.9531 | 24.209 | ||
| 31/32 | 0.9688 | 24.606 | ||
| 63/64 | 0.9844 | 25.003 | ||
| 1 | 1.0000 | 25.400 | ||
No size matches that. Clear the filter to see the full table.
Sources mapped to columns
One line per source, listing exactly which columns it covers. A column cannot appear in the table without appearing here, because the build fails on it.
| Columns | Source | Basis |
|---|---|---|
| Size Diameter in Diameter mm | Fractional sizes and the inch A fractional bit size IS its decimal value: 3/16 in = 0.1875 in. The millimetre column is that value × 25.4, which is the exact definition of the inch. | Definition |
Conditions
- Nominal bit sizes. A drilled hole runs slightly oversize depending on the bit, the material and the setup.
Recomputed from the definitions above on every build · last build audit 2026-08-17
Where the equipment manufacturer specifies a figure for the specific assembly, that figure governs. This is a reference sheet, not a substitute for the instructions that came with the part.
The four drill size series
"Drill bit size" covers four separate series. Only the fractional series is arithmetic. The other three are published tables, and they go up when each has been read against the standard.
- Fractional (64ths)On this pageFractional sizes and the inch
- Number sizes (1–80)In verificationANSI/ASME B94.11M
- Letter sizes (A–Z)In verificationANSI/ASME B94.11M
- Metric sizesIn verificationISO 235
One data set. Two purpose-built sheets.
The printable sheet and the vertical image use different layouts, so neither one sacrifices readability to the other.
Download PDF 
Download PNG Both sheets carry every column that is on the page.
How to use this chart
- Find the fractional size, or filter by a decimal or millimetre value to find the nearest bit.
- There is no separate decimal column because for a fractional bit the two are the same number: 3/16 in is 0.1875 in.
- This page carries the fractional series. The number, letter and metric series are published tables rather than arithmetic, so they are in verification and not on the site yet: see the four series listed below.
Frequently asked questions
How is this different from the fraction to decimal chart?
Same arithmetic, different purpose. This page is a bit list: the sizes an index actually contains, for choosing a drill. The conversion chart adds the count of 64ths and thousandths, for reading a tape measure or a micrometer.
Why are drill sizes in 64ths?
A 1/64 in step is fine enough that the next size up is a workable second choice, and coarse enough that a full index stays a manageable number of bits.
Will a bit drill a hole exactly its own size?
Usually slightly oversize. How much depends on the bit, the material, the setup rigidity and whether the hole was centre-drilled first. For a hole that has to hold a dimension, drill under and ream or bore to size.