Tap drill calculator

Type a thread such as 1/4-20, #10-32 or M6x1 to get the tap drill size. The calculator uses the standard formula for about 75% thread, drill = major diameter − 0.974 × pitch, then shows the nearest drill in each size system and the thread percentage each one leaves. Charts usually choose the nearest common drill, so a listed size can differ from the exact figure by a few thousandths.

UNC (coarse) threads

Tap	Drill	Decimal (in)
#4-40	#43	0.0890
#6-32	#36	0.1065
#8-32	#29	0.1360
#10-24	#25	0.1495
#12-24	#16	0.1770
1/4-20	#7	0.2010
5/16-18	F	0.2570
3/8-16	5/16	0.3125
7/16-14	U	0.3680
1/2-13	27/64	0.4219
9/16-12	31/64	0.4844
5/8-11	17/32	0.5313
3/4-10	21/32	0.6563
7/8-9	49/64	0.7656
1-8	7/8	0.8750

UNF (fine) threads

Tap	Drill	Decimal (in)
#4-48	#42	0.0935
#6-40	#33	0.1130
#8-36	#29	0.1360
#10-32	#21	0.1590
#12-28	#14	0.1820
1/4-28	#3	0.2130
5/16-24	I	0.2720
3/8-24	Q	0.3320
7/16-20	25/64	0.3906
1/2-20	29/64	0.4531
9/16-18	33/64	0.5156
5/8-18	37/64	0.5781
3/4-16	11/16	0.6875
7/8-14	13/16	0.8125
1-12	59/64	0.9219

Metric coarse threads

Tap	Drill	Size (mm)
M3 x 0.5	2.5 mm	2.5
M4 x 0.7	3.3 mm	3.3
M5 x 0.8	4.2 mm	4.2
M6 x 1.0	5.0 mm	5.0
M8 x 1.25	6.8 mm	6.8
M10 x 1.5	8.5 mm	8.5
M12 x 1.75	10.2 mm	10.2
M14 x 2.0	12.0 mm	12.0
M16 x 2.0	14.0 mm	14.0
M20 x 2.5	17.5 mm	17.5

Using a tap drill

Choose a lower thread percentage for hard metals such as stainless and tool steel: 60 to 65% is much easier to tap and only slightly weaker.
Drill straight and deburr the hole before tapping, and use cutting oil in steel.
For a bolt that passes through, you need a clearance hole instead, larger than the bolt; the 1/4-20 tap drill and clearance hole guide gives an example.

Print the chart: printable tap drill chart. Pipe threads (NPT) and more sizes are in the tap drill size chart. Every number, letter and metric drill is in the drill bit size chart. To set the drill speed for the hole, use the drill speed calculator.