Drill Size Chart.
Complete drill size reference with metric, fractional, number, and letter drills. Search by hole size, thread, or drill designation. Includes tap drill and clearance hole columns for every common thread.
| Designation | Decimal (mm) | Decimal (in) | Common use |
|---|
Drill Size Reference
Drill sizes come in four overlapping systems: metric (mm), fractional inch, number drills (#1-#80), and letter drills (A-Z). Engineers and machinists need to cross-reference between them constantly.
Drill Size Systems
- Metric (mm): 0.1 mm increments below 1 mm; 0.05 mm increments common above
- Fractional inch: 1/64" increments — 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, etc.
- Number drills: #80 (smallest, 0.0135") to #1 (0.228") — non-linear spacing
- Letter drills: A (0.234") to Z (0.413") — for sizes between 1/4" and 1/2"
Common Tap Drill Sizes — Metric Coarse
| Thread | Tap drill | Clearance |
|---|---|---|
| M3 × 0.5 | 2.5 mm | 3.4 mm |
| M4 × 0.7 | 3.3 mm | 4.5 mm |
| M5 × 0.8 | 4.2 mm | 5.5 mm |
| M6 × 1.0 | 5.0 mm | 6.6 mm |
| M8 × 1.25 | 6.8 mm | 9.0 mm |
| M10 × 1.5 | 8.5 mm | 11.0 mm |
| M12 × 1.75 | 10.2 mm | 13.5 mm |
Drill Tolerance Cautions
- New drill ≠ used drill: drills wear; 0.05-0.1 mm reduction common.
- Drill drift: small drills wander, hole position can shift 0.1-0.3 mm.
- Hole growth: drilled holes are typically 0.05-0.10 mm larger than drill diameter.
- Use a CMM for tolerance-critical hole verification — pin gauges only verify minimum.
Related Tools
For thread series details, Thread Pitch Reference. For position tolerance verification, Position Tolerance. For ISO fits, ISO 286 Fits.