Complete Drill Bit Size Chart
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Your comprehensive reference for fractional, number, letter, and metric drill bit sizes. Includes tap drill sizes, clearance holes, and pilot hole recommendations.
Photo via Unsplash
Your comprehensive reference for fractional, number, letter, and metric drill bit sizes. Includes tap drill sizes, clearance holes, and pilot hole recommendations.
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| Size | Decimal (in) | Millimeters | Type |
|---|
Use these drill sizes before tapping threads. Based on 75% thread engagement (standard practice).
| Thread | Tap Drill | Decimal |
|---|---|---|
| 4-40 | #43 | 0.089" |
| 6-32 | #36 | 0.1065" |
| 8-32 | #29 | 0.136" |
| 10-24 | #25 | 0.1495" |
| 10-32 | #21 | 0.159" |
| 1/4-20 | #7 | 0.201" |
| 5/16-18 | F | 0.257" |
| 3/8-16 | 5/16" | 0.3125" |
| 7/16-14 | U | 0.368" |
| 1/2-13 | 27/64" | 0.4219" |
| 5/8-11 | 17/32" | 0.5313" |
| 3/4-10 | 21/32" | 0.6563" |
| Thread | Tap Drill | Decimal |
|---|---|---|
| M3 x 0.5 | 2.5mm | 0.098" |
| M4 x 0.7 | 3.3mm | 0.130" |
| M5 x 0.8 | 4.2mm | 0.165" |
| M6 x 1.0 | 5.0mm | 0.197" |
| M8 x 1.25 | 6.8mm | 0.268" |
| M10 x 1.5 | 8.5mm | 0.335" |
| M12 x 1.75 | 10.2mm | 0.402" |
| M14 x 2.0 | 12.0mm | 0.472" |
| M16 x 2.0 | 14.0mm | 0.551" |
| M20 x 2.5 | 17.5mm | 0.689" |
Use these drill sizes when the bolt needs to pass through freely (not threaded).
| Bolt Size | Close Fit | Free Fit |
|---|---|---|
| #4 | 1/8" | 9/64" |
| #6 | 9/64" | 5/32" |
| #8 | 11/64" | 3/16" |
| #10 | 13/64" | 7/32" |
| 1/4" | 17/64" | 9/32" |
| 5/16" | 21/64" | 11/32" |
| 3/8" | 25/64" | 13/32" |
| 7/16" | 29/64" | 15/32" |
| 1/2" | 17/32" | 9/16" |
| 5/8" | 21/32" | 11/16" |
| 3/4" | 25/32" | 13/16" |
| Bolt Size | Close Fit | Free Fit |
|---|---|---|
| M3 | 3.2mm | 3.4mm |
| M4 | 4.3mm | 4.5mm |
| M5 | 5.3mm | 5.5mm |
| M6 | 6.4mm | 6.6mm |
| M8 | 8.4mm | 9.0mm |
| M10 | 10.5mm | 11.0mm |
| M12 | 13.0mm | 14.0mm |
| M14 | 15.0mm | 16.0mm |
| M16 | 17.0mm | 18.0mm |
| M20 | 21.0mm | 22.0mm |
Pilot holes prevent splitting and make driving easier. Use smaller size for softwood, larger for hardwood.
| Screw Size | Softwood Pilot | Hardwood Pilot | Shank Hole | Countersink |
|---|---|---|---|---|
| #2 | 1/16" | 1/16" | 3/32" | 3/16" |
| #3 | 1/16" | 5/64" | 7/64" | 1/4" |
| #4 | 1/16" | 5/64" | 7/64" | 1/4" |
| #5 | 5/64" | 3/32" | 1/8" | 1/4" |
| #6 | 5/64" | 3/32" | 9/64" | 5/16" |
| #7 | 3/32" | 7/64" | 5/32" | 5/16" |
| #8 | 3/32" | 7/64" | 11/64" | 3/8" |
| #9 | 7/64" | 1/8" | 3/16" | 3/8" |
| #10 | 7/64" | 1/8" | 3/16" | 3/8" |
| #12 | 1/8" | 9/64" | 7/32" | 7/16" |
| #14 | 9/64" | 5/32" | 1/4" | 1/2" |
Number drill bits range from #1 (0.228") to #80 (0.0135"), with higher numbers being smaller. Letter drill bits range from A (0.234") to Z (0.413"), with later letters being larger. Together they fill in the gaps between fractional sizes, providing more precise sizing options for tap drills and close-tolerance work.
To convert metric drill sizes to inches, divide the millimeter size by 25.4. For example, a 6mm drill bit equals 6 / 25.4 = 0.236 inches. Our chart includes both metric and imperial equivalents for easy reference. For quick mental math, 25mm is almost exactly 1 inch, and 1mm is about 0.040 inches.
For softwood like pine or cedar, use a pilot hole about 60-70% of the screw's root diameter. For hardwood like oak or maple, use 80-90%. For example, a #8 wood screw typically needs a 3/32" pilot hole in softwood or 7/64" in hardwood. Always drill a shank hole the same diameter as the screw shank where the non-threaded portion will sit.
A tap drill creates a hole that will be threaded with a tap. The correct size depends on the thread size and desired engagement percentage. Standard practice is 75% thread engagement, which provides near-full strength (about 98%) while being much easier to tap than 100%. Use our tap drill chart above or the formula: Tap Drill = Major Diameter - (1 / TPI) for inch threads, or Major Diameter - Pitch for metric.