#15 drill bit size
0.18 in
4.57 mm · number drill
| Inches | 0.18 in |
| Millimetres | 4.57 mm |
| Nearest metric drill | 4.6 mm |
| System | Number (#1 to #60) |
What #15 means
A bit marked #15 is a number drill, and the number is an index rather than a measurement — the higher the number, the smaller the bit. #1 is 0.228 inches and #60 is 0.04. That is the opposite of the fractional sizes stamped on a home set, which is why a number drill and a fraction of similar appearance can be very different holes.
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 #15:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.054 in larger |
| fractional | 3/16" — 0.1875 in | 0.0075 in larger |
| metric | 4.6 mm | 0.028 mm larger |
The closest substitute is 0.0075 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 0.18 inches
The busiest part of the number series. Tapping drills for machine screws from #4 to #12 sit in here, along with pilot holes for wood screws and clearance for small pins. If a number drill in a workshop is worn out, it is usually one of these.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| 11/64" | 0.1719 in | 4.37 mm |
| #17 | 0.173 in | 4.39 mm |
| #16 | 0.177 in | 4.5 mm |
| #15 | 0.18 in | 4.57 mm |
| #14 | 0.182 in | 4.62 mm |
| #13 | 0.185 in | 4.7 mm |
| 3/16" | 0.1875 in | 4.76 mm |
Frequently asked questions
What size is a #15 drill bit?
0.18 inches, which is 4.57 mm. Number drills run from #1 at 0.228 inches down to #60 at 0.04, getting smaller as the number rises — the opposite of what most people expect the first time.
What is a #15 drill bit in mm?
4.57 mm. A metric index will offer 4.6 mm as the nearest stocked size, which is 0.028 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is #15 a tapping drill size?
Not for any of the unified threads on this site. The next size up, #14, is the tapping drill for 12-28.
What is the next size up from #15?
#14 at 0.182 inches — 0.002 inches larger. Below it is #16 at 0.177.
Other sizes
- #14 drill bit — 0.182 in, 4.62 mm
- #13 drill bit — 0.185 in, 4.7 mm
- 3/16" drill bit — 0.1875 in, 4.76 mm
- #12 drill bit — 0.189 in, 4.8 mm
- #11 drill bit — 0.191 in, 4.85 mm
- #10 drill bit — 0.1935 in, 4.91 mm
- #9 drill bit — 0.196 in, 4.98 mm
- #8 drill bit — 0.199 in, 5.05 mm