Drill Size Chart & Tap Drill Chart

Lists number (#80 to #1), letter (A to Z), fractional inch and metric drills in one chart sorted by diameter, in inches and mm, with tap drills for common threads and clearance holes for bolts. Use it to convert inch drills to mm or to choose a tap drill.

How to use

1. On "Drill sizes", enter a diameter in mm or inches under "Find the nearest drill" to see the matching drill and the next smaller and larger ones.
2. Type a drill name such as #7, F, 17/64 or 6.8 in "Search the chart" to narrow the chart.
3. On "Tap drills", choose a "Thread type" to see the "Common tap drill" and "Thread %" for each thread. Use the "Thread % calculator" for the drill you have.
4. For holes that a bolt passes through, use "Clearance holes" and pick fine, medium or coarse.

How it works

• Number and letter drills are the inch values of ASME B94.11M, converted at 1 in = 25.4 mm. Fractional drills go to 1 in in 1/64 in steps; metric drills cover 0.5–13 mm in 0.1 mm steps and 13.5–20 mm in 0.5 mm steps.
• The tap drill tables cover metric coarse and fine M1 to M30, UNC, UNF, NPT and G and Rc pipe threads. Only values on which two sources agree are included.
• Thread % = (D − d) ÷ (0.01299 × P), where D is the major diameter, d the drill and P the pitch. A drill of D − P gives about 77%.

Questions and answers

What size drill do I need for an M6 tap?

5 mm. For metric coarse threads, subtract the pitch from the diameter: M6×1 is 6 − 1 = 5 mm. The chart gives 6.8 mm for M8×1.25 and 8.5 mm for M10×1.5.

What is the tap drill for 1/4-20 UNC?

A #7 drill (0.201 in, about 5.11 mm). For 1/4-28 UNF it is a #3 drill.

What is an F drill in mm?

0.257 in, about 6.53 mm. Search any letter or number drill by name to see both inches and mm.

What clearance hole does an M6 bolt need?

Under ISO 273: 6.4 mm fine, 6.6 mm medium and 7 mm coarse. Medium is the usual choice.