Standard Drill Bit Sizes
Drill bits come in four sizing systems: fractional inches, wire-gauge numbers from #80 to #1, letters from A to Z, and millimetres. Enter any size — 1/4, #29, F, 6.5 mm or a decimal like 0.201 — and the converter shows the exact decimal and metric diameter and the nearest bits in every other system, plus tap drill sizes for common threads.
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Drill size converter
Drill Size Charts
Printable drill charts: number and letter drill sizes with decimal and metric equivalents, fractional sizes to 1/2″, a tap drill chart for UNC, UNF and metric threads, and clearance hole sizes — workshop wall format.
- Number drills (PDF/XLSX)
- Letter & fractional (PDF)
- Tap drills (PDF)
- Clearance holes (PDF)
Formats: PDF, XLSX. Instant download after payment (link valid 72 hours, up to 5 downloads). AI-assisted: the templates were drafted with AI help and reviewed and laid out before publishing.
$3.00 USD, one-time 4 files · about $0.75 each
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Free sample: Clearance Hole Chart (PDF, 73 KB)
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The four drill size systems
| System | Range | Steps |
|---|---|---|
| Fractional inch | 1/64″ upwards | 1/64″ increments in most sets |
| Number (wire gauge) | #80 (0.0135″) to #1 (0.228″) | Larger numbers are smaller drills |
| Letter | A (0.234″) to Z (0.413″) | Continues above #1 |
| Metric | 0.5 mm upwards | Often 0.1 mm or 0.5 mm steps |
Number and letter drills fill the gaps between fractional sizes, which is why they are used for tap drills, clearance holes and precision work.
Number drill sizes
| # | Inches | # | Inches | # | Inches | # | Inches |
|---|---|---|---|---|---|---|---|
| #1 | 0.2280 | #21 | 0.1590 | #41 | 0.0960 | #61 | 0.0390 |
| #2 | 0.2210 | #22 | 0.1570 | #42 | 0.0935 | #62 | 0.0380 |
| #3 | 0.2130 | #23 | 0.1540 | #43 | 0.0890 | #63 | 0.0370 |
| #4 | 0.2090 | #24 | 0.1520 | #44 | 0.0860 | #64 | 0.0360 |
| #5 | 0.2055 | #25 | 0.1495 | #45 | 0.0820 | #65 | 0.0350 |
| #6 | 0.2040 | #26 | 0.1470 | #46 | 0.0810 | #66 | 0.0330 |
| #7 | 0.2010 | #27 | 0.1440 | #47 | 0.0785 | #67 | 0.0320 |
| #8 | 0.1990 | #28 | 0.1405 | #48 | 0.0760 | #68 | 0.0310 |
| #9 | 0.1960 | #29 | 0.1360 | #49 | 0.0730 | #69 | 0.0292 |
| #10 | 0.1935 | #30 | 0.1285 | #50 | 0.0700 | #70 | 0.0280 |
| #11 | 0.1910 | #31 | 0.1200 | #51 | 0.0670 | #71 | 0.0260 |
| #12 | 0.1890 | #32 | 0.1160 | #52 | 0.0635 | #72 | 0.0250 |
| #13 | 0.1850 | #33 | 0.1130 | #53 | 0.0595 | #73 | 0.0240 |
| #14 | 0.1820 | #34 | 0.1110 | #54 | 0.0550 | #74 | 0.0225 |
| #15 | 0.1800 | #35 | 0.1100 | #55 | 0.0520 | #75 | 0.0210 |
| #16 | 0.1770 | #36 | 0.1065 | #56 | 0.0465 | #76 | 0.0200 |
| #17 | 0.1730 | #37 | 0.1040 | #57 | 0.0430 | #77 | 0.0180 |
| #18 | 0.1695 | #38 | 0.1015 | #58 | 0.0420 | #78 | 0.0160 |
| #19 | 0.1660 | #39 | 0.0995 | #59 | 0.0410 | #79 | 0.0145 |
| #20 | 0.1610 | #40 | 0.0980 | #60 | 0.0400 | #80 | 0.0135 |
Letter drill sizes
| Letter | Inches | mm |
|---|---|---|
| A | 0.234 | 5.94 |
| B | 0.238 | 6.05 |
| C | 0.242 | 6.15 |
| D | 0.246 | 6.25 |
| E | 0.250 | 6.35 |
| F | 0.257 | 6.53 |
| G | 0.261 | 6.63 |
| H | 0.266 | 6.76 |
| I | 0.272 | 6.91 |
| J | 0.277 | 7.04 |
| K | 0.281 | 7.14 |
| L | 0.290 | 7.37 |
| M | 0.295 | 7.49 |
| N | 0.302 | 7.67 |
| O | 0.316 | 8.03 |
| P | 0.323 | 8.20 |
| Q | 0.332 | 8.43 |
| R | 0.339 | 8.61 |
| S | 0.348 | 8.84 |
| T | 0.358 | 9.09 |
| U | 0.368 | 9.35 |
| V | 0.377 | 9.58 |
| W | 0.386 | 9.80 |
| X | 0.397 | 10.08 |
| Y | 0.404 | 10.26 |
| Z | 0.413 | 10.49 |
Tap drill chart
| Thread | Tap drill | Decimal (in) |
|---|---|---|
| #4-40 UNC | #43 | 0.089 |
| #6-32 UNC | #36 | 0.1065 |
| #8-32 UNC | #29 | 0.136 |
| #10-24 UNC | #25 | 0.1495 |
| #10-32 UNF | #21 | 0.159 |
| 1/4-20 UNC | #7 | 0.201 |
| 1/4-28 UNF | #3 | 0.213 |
| 5/16-18 UNC | F | 0.257 |
| 5/16-24 UNF | I | 0.272 |
| 3/8-16 UNC | 5/16 | 0.3125 |
| 3/8-24 UNF | Q | 0.332 |
| 7/16-14 UNC | U | 0.368 |
| 7/16-20 UNF | 25/64 | 0.3906 |
| 1/2-13 UNC | 27/64 | 0.4219 |
| 1/2-20 UNF | 29/64 | 0.4531 |
| M3 × 0.5 | 2.5 mm | 0.0984 |
| M4 × 0.7 | 3.3 mm | 0.1299 |
| M5 × 0.8 | 4.2 mm | 0.1654 |
| M6 × 1.0 | 5.0 mm | 0.1969 |
| M8 × 1.25 | 6.8 mm | 0.2677 |
| M10 × 1.5 | 8.5 mm | 0.3346 |
| M12 × 1.75 | 10.2 mm | 0.4016 |
Tap drills shown give roughly 75% thread engagement, the usual general-purpose choice. For hard materials or deep holes, a slightly larger drill reduces tapping torque.
How to use the converter
- Type a size in any system: 1/4, 7/64, #29, F, 6.5mm, or a decimal such as 0.201 (values above 2 are read as millimetres).
- Read the exact decimal and metric diameter.
- See the nearest bits in every other system, with the difference in thousandths of an inch.
- If the size is a standard tap drill, the matching threads are listed.
Worked example
A #7 drill is 0.201″ (5.105 mm) — the standard tap drill for a 1/4-20 UNC thread. The nearest fractional size is 13/64″ (0.2031″), just 2 thousandths larger, and the nearest metric bit is 5.1 mm. If you don’t have a #7, a 13/64″ bit works for most tapping in soft materials.
Clearance holes
| Screw | Close fit | Free fit |
|---|---|---|
| #6 | #28 (0.1405″) | #25 (0.1495″) |
| #8 | #19 (0.166″) | #16 (0.177″) |
| #10 | #11 (0.191″) | #7 (0.201″) |
| 1/4″ | F (0.257″) | H (0.266″) |
| M4 | 4.3 mm | 4.5 mm |
| M5 | 5.3 mm | 5.5 mm |
| M6 | 6.4 mm | 6.6 mm |
Close fit gives accurate location; free fit allows for slight misalignment.
Drilling tips
- Centre-punch before drilling so the bit doesn’t wander.
- Use slower speeds for larger bits and harder metals.
- Use cutting fluid for steel and a pilot hole for bits above about 3/8″.
- Keep bits sharp — a dull bit makes oversized, rough holes.
- Measure bits with calipers; markings wear off.
Frequently asked questions
What size is a #7 drill bit?
0.201 inches (5.1 mm), the tap drill for 1/4-20.
What is an F drill bit?
0.257 inches (6.53 mm), the tap drill for 5/16-18.
Which is bigger, #1 or #80?
#1 (0.228″) is much larger than #80 (0.0135″).
What drill size for an M6 tap?
5.0 mm.
What is 1/4 inch in mm?
6.35 mm.
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