Drill bit size chart

Every numbered and letter drill size in decimal inches and millimeters. Wire-gauge sizes fill the gaps between fractional drills — they are how machinists hit tap-drill sizes and close fits without grinding anything custom.

Number drills #80 → #1

Drill	Inches	mm	Drill	Inches	mm
#80	0.0135	0.343	#40	0.0980	2.489
#79	0.0145	0.368	#39	0.0995	2.527
#78	0.0160	0.406	#38	0.1015	2.578
#77	0.0180	0.457	#37	0.1040	2.642
#76	0.0200	0.508	#36	0.1065	2.705
#75	0.0210	0.533	#35	0.1100	2.794
#74	0.0225	0.571	#34	0.1110	2.819
#73	0.0240	0.610	#33	0.1130	2.870
#72	0.0250	0.635	#32	0.1160	2.946
#71	0.0260	0.660	#31	0.1200	3.048
#70	0.0280	0.711	#30	0.1285	3.264
#69	0.0292	0.742	#29	0.1360	3.454
#68	0.0310	0.787	#28	0.1405	3.569
#67	0.0320	0.813	#27	0.1440	3.658
#66	0.0330	0.838	#26	0.1470	3.734
#65	0.0350	0.889	#25	0.1495	3.797
#64	0.0360	0.914	#24	0.1520	3.861
#63	0.0370	0.940	#23	0.1540	3.912
#62	0.0380	0.965	#22	0.1570	3.988
#61	0.0390	0.991	#21	0.1590	4.039
#60	0.0400	1.016	#20	0.1610	4.089
#59	0.0410	1.041	#19	0.1660	4.216
#58	0.0420	1.067	#18	0.1695	4.305
#57	0.0430	1.092	#17	0.1730	4.394
#56	0.0465	1.181	#16	0.1770	4.496
#55	0.0520	1.321	#15	0.1800	4.572
#54	0.0550	1.397	#14	0.1820	4.623
#53	0.0595	1.511	#13	0.1850	4.699
#52	0.0635	1.613	#12	0.1890	4.801
#51	0.0670	1.702	#11	0.1910	4.851
#50	0.0700	1.778	#10	0.1935	4.915
#49	0.0730	1.854	#9	0.1960	4.978
#48	0.0760	1.930	#8	0.1990	5.055
#47	0.0785	1.994	#7	0.2010	5.105
#46	0.0810	2.057	#6	0.2040	5.182
#45	0.0820	2.083	#5	0.2055	5.220
#44	0.0860	2.184	#4	0.2090	5.309
#43	0.0890	2.261	#3	0.2130	5.410
#42	0.0935	2.375	#2	0.2210	5.613
#41	0.0960	2.438	#1	0.2280	5.791

Letter drills A → Z

Drill	Inches	mm	Drill	Inches	mm
A	0.2340	5.944	N	0.3020	7.671
B	0.2380	6.045	O	0.3160	8.026
C	0.2420	6.147	P	0.3230	8.204
D	0.2460	6.248	Q	0.3320	8.433
E	0.2500	6.350	R	0.3390	8.611
F	0.2570	6.528	S	0.3480	8.839
G	0.2610	6.629	T	0.3580	9.093
H	0.2660	6.756	U	0.3680	9.347
I	0.2720	6.909	V	0.3770	9.576
J	0.2770	7.036	W	0.3860	9.804
K	0.2810	7.137	X	0.3970	10.084
L	0.2900	7.366	Y	0.4040	10.262
M	0.2950	7.493	Z	0.4130	10.490

Reading the chart in practice

If a drawing calls out a metric hole and you only have inch drills (or the reverse), find the closest row above rather than converting in your head — the nearest standard drill is usually within a few hundredths of a millimeter. For threaded holes, use the tap drill chart instead; it picks the right wire-gauge size for you.

Frequently asked questions

Why do number drills skip around so much?

The series grew out of the wire gauge it was named after: each number originally matched a wire diameter, and manufacturers standardized on those arbitrary steps rather than a formula. That is why #56 (0.0465") jumps twice as far as #57 (0.043"), and why there is no clean equation behind the table.

Which is bigger, a #7 or a #1 drill?

#1. Numbered drill sizes run opposite to intuition: higher numbers are smaller, from #80 at 0.0135" up to #1 at 0.228". Letter drills continue upward past that, ending with Z at 0.413".

How exact are the millimeter values?

Each millimeter value here is the decimal inch figure multiplied by exactly 25.4 mm per inch. Real drills are ground to plus-or-minus tolerances that depend on manufacturer and diameter class, so treat the last digit as nominal.

Sizes per ANSI/ASME B94.11M as published in standard drill charts; millimeter values are exact conversions of the tabulated inch figures.