5/8" drill bit size
0.625 in
15.88 mm · fractional drill
| Inches | 0.625 in |
| Millimetres | 15.88 mm |
| Nearest metric drill | 15.9 mm |
| System | Fractional (64ths) |
What 5/8" means
5/8" is a fractional drill, stepping in 64ths of an inch. Fractional sizes are the coarsest of the three systems, which is why a fractional set alone cannot hit most tapping sizes and why number and letter drills exist at all.
The same hole in the other systems
Three drill systems overlap across this range and a workshop rarely has all three. The nearest bit of each other kind to 5/8":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.397 in smaller |
| letter | Z — 0.413 in | 0.212 in smaller |
| metric | 15.9 mm | 0.025 mm larger |
The closest substitute is 0.212 inches away. For a clearance hole that is nothing; for a tapping hole it moves the thread engagement by several per cent, which is the difference between an easy tap and a broken one.
What gets drilled at 0.625 inches
Half an inch and up is where twist drills stop being the obvious tool. A bit this size in mild steel needs a pilot, a slow speed and something to hold the work; past three-quarters of an inch most people reach for a hole saw or a step drill instead.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| 37/64" | 0.5781 in | 14.68 mm |
| 19/32" | 0.5938 in | 15.08 mm |
| 39/64" | 0.6094 in | 15.48 mm |
| 5/8" | 0.625 in | 15.88 mm |
| 41/64" | 0.6406 in | 16.27 mm |
| 21/32" | 0.6563 in | 16.67 mm |
| 43/64" | 0.6719 in | 17.07 mm |
Frequently asked questions
What size is a 5/8" drill bit?
0.625 inches, which is 15.88 mm. Fractional drills step in 64ths of an inch, which is the coarsest of the three systems and the one most home sets contain.
What is a 5/8" drill bit in mm?
15.88 mm. A metric index will offer 15.9 mm as the nearest stocked size, which is 0.025 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is 5/8" a tapping drill size?
Not for any of the unified threads on this site. It sits between the sizes the standard taps call for, so it is a clearance or pilot drill rather than a tapping one.
What is the next size up from 5/8"?
41/64" at 0.6406 inches — 0.0156 inches larger. Below it is 39/64" at 0.6094.
Other sizes
- 41/64" drill bit — 0.6406 in, 16.27 mm
- 21/32" drill bit — 0.6563 in, 16.67 mm
- 43/64" drill bit — 0.6719 in, 17.07 mm
- 11/16" drill bit — 0.6875 in, 17.46 mm
- 45/64" drill bit — 0.7031 in, 17.86 mm
- 23/32" drill bit — 0.7188 in, 18.26 mm
- 47/64" drill bit — 0.7344 in, 18.65 mm
- 3/4" drill bit — 0.75 in, 19.05 mm