1/2" drill bit size
0.5 in
12.7 mm · fractional drill
| Inches | 0.5 in |
| Millimetres | 12.7 mm |
| Nearest metric drill | 12.7 mm |
| System | Fractional (64ths) |
What 1/2" means
1/2" 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 1/2":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.272 in smaller |
| letter | Z — 0.413 in | 0.087 in smaller |
| metric | 12.7 mm | identical |
The closest substitute is 0.087 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 0.5 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 |
|---|---|---|
| 29/64" | 0.4531 in | 11.51 mm |
| 15/32" | 0.4688 in | 11.91 mm |
| 31/64" | 0.4844 in | 12.3 mm |
| 1/2" | 0.5 in | 12.7 mm |
| 33/64" | 0.5156 in | 13.1 mm |
| 17/32" | 0.5313 in | 13.49 mm |
| 35/64" | 0.5469 in | 13.89 mm |
Frequently asked questions
What size is a 1/2" drill bit?
0.5 inches, which is 12.7 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 1/2" drill bit in mm?
12.7 mm. A metric index will offer 12.7 mm as the nearest stocked size, which is near enough identical.
Is 1/2" a tapping drill size?
Not for any of the unified threads on this site. The next size up, 33/64", is the tapping drill for 9/16-18.
What is the next size up from 1/2"?
33/64" at 0.5156 inches — 0.0156 inches larger. Below it is 31/64" at 0.4844.
Other sizes
- 33/64" drill bit — 0.5156 in, 13.1 mm
- 17/32" drill bit — 0.5313 in, 13.49 mm
- 35/64" drill bit — 0.5469 in, 13.89 mm
- 9/16" drill bit — 0.5625 in, 14.29 mm
- 37/64" drill bit — 0.5781 in, 14.68 mm
- 19/32" drill bit — 0.5938 in, 15.08 mm
- 39/64" drill bit — 0.6094 in, 15.48 mm
- 5/8" drill bit — 0.625 in, 15.88 mm