Number and Letter Drill Size Chart

Besides fractional bits (1/16, 1/8, 1/4 …), US drill sets come in two more series: number drills, from #80 (tiny) to #1, and letter drills, from A to Z. Together they fill the gaps between 1/64 inch steps, so there’s a bit for every tap drill and clearance hole.

The three series fit end to end:

• Number drills: #80 = 0.0135 in up to #1 = 0.228 in. The bigger the number, the smaller the drill.
• Letter drills: A = 0.234 in up to Z = 0.413 in, continuing where the numbers stop.
• Fractional drills: 1/64 in steps, overlapping both. A 1/4 in bit is the same as an E.

Number drill sizes #1 to #40

Drill	Decimal (in)	mm	Nearest fraction
#1	0.2280	5.79	15/64 (0.2344)
#2	0.2210	5.61	7/32 (0.2188)
#3	0.2130	5.41	7/32 (0.2188)
#4	0.2090	5.31	13/64 (0.2031)
#5	0.2055	5.22	13/64 (0.2031)
#6	0.2040	5.18	13/64 (0.2031)
#7	0.2010	5.11	13/64 (0.2031)
#8	0.1990	5.05	13/64 (0.2031)
#9	0.1960	4.98	13/64 (0.2031)
#10	0.1935	4.91	3/16 (0.1875)
#11	0.1910	4.85	3/16 (0.1875)
#12	0.1890	4.80	3/16 (0.1875)
#13	0.1850	4.70	3/16 (0.1875)
#14	0.1820	4.62	3/16 (0.1875)
#15	0.1800	4.57	3/16 (0.1875)
#16	0.1770	4.50	11/64 (0.1719)
#17	0.1730	4.39	11/64 (0.1719)
#18	0.1695	4.31	11/64 (0.1719)
#19	0.1660	4.22	11/64 (0.1719)
#20	0.1610	4.09	5/32 (0.1563)
#21	0.1590	4.04	5/32 (0.1563)
#22	0.1570	3.99	5/32 (0.1563)
#23	0.1540	3.91	5/32 (0.1563)
#24	0.1520	3.86	5/32 (0.1563)
#25	0.1495	3.80	5/32 (0.1563)
#26	0.1470	3.73	9/64 (0.1406)
#27	0.1440	3.66	9/64 (0.1406)
#28	0.1405	3.57	9/64 (0.1406)
#29	0.1360	3.45	9/64 (0.1406)
#30	0.1285	3.26	1/8 (0.1250)
#31	0.1200	3.05	1/8 (0.1250)
#32	0.1160	2.95	7/64 (0.1094)
#33	0.1130	2.87	7/64 (0.1094)
#34	0.1110	2.82	7/64 (0.1094)
#35	0.1100	2.79	7/64 (0.1094)
#36	0.1065	2.71	7/64 (0.1094)
#37	0.1040	2.64	7/64 (0.1094)
#38	0.1015	2.58	3/32 (0.0938)
#39	0.0995	2.53	3/32 (0.0938)
#40	0.0980	2.49	3/32 (0.0938)

Number drill sizes #41 to #80

Drill	Decimal (in)	mm	Nearest fraction
#41	0.0960	2.44	3/32 (0.0938)
#42	0.0935	2.37	3/32 (0.0938)
#43	0.0890	2.26	3/32 (0.0938)
#44	0.0860	2.18	3/32 (0.0938)
#45	0.0820	2.08	5/64 (0.0781)
#46	0.0810	2.06	5/64 (0.0781)
#47	0.0785	1.99	5/64 (0.0781)
#48	0.0760	1.93	5/64 (0.0781)
#49	0.0730	1.85	5/64 (0.0781)
#50	0.0700	1.78	1/16 (0.0625)
#51	0.0670	1.70	1/16 (0.0625)
#52	0.0635	1.61	1/16 (0.0625)
#53	0.0595	1.51	1/16 (0.0625)
#54	0.0550	1.40	1/16 (0.0625)
#55	0.0520	1.32	3/64 (0.0469)
#56	0.0465	1.18	3/64 (0.0469)
#57	0.0430	1.09	3/64 (0.0469)
#58	0.0420	1.07	3/64 (0.0469)
#59	0.0410	1.04	3/64 (0.0469)
#60	0.0400	1.02	3/64 (0.0469)
#61	0.0390	0.99	1/32 (0.0313)
#62	0.0380	0.97	1/32 (0.0313)
#63	0.0370	0.94	1/32 (0.0313)
#64	0.0360	0.91	1/32 (0.0313)
#65	0.0350	0.89	1/32 (0.0313)
#66	0.0330	0.84	1/32 (0.0313)
#67	0.0320	0.81	1/32 (0.0313)
#68	0.0310	0.79	1/32 (0.0313)
#69	0.0292	0.74	1/32 (0.0313)
#70	0.0280	0.71	1/32 (0.0313)
#71	0.0260	0.66	1/32 (0.0313)
#72	0.0250	0.64	1/32 (0.0313)
#73	0.0240	0.61	1/32 (0.0313)
#74	0.0225	0.57	1/64 (0.0156)
#75	0.0210	0.53	1/64 (0.0156)
#76	0.0200	0.51	1/64 (0.0156)
#77	0.0180	0.46	1/64 (0.0156)
#78	0.0160	0.41	1/64 (0.0156)
#79	0.0145	0.37	1/64 (0.0156)
#80	0.0135	0.34	1/64 (0.0156)

The small sizes, #61 to #80, are for jewelry, model making, electronics and clock work, and are usually sold as a set in a pin vise.

Letter drill sizes A to Z

Drill	Decimal (in)	mm	Nearest fraction
A	0.234	5.94	15/64 (0.2344)
B	0.238	6.05	15/64 (0.2344)
C	0.242	6.15	15/64 (0.2344)
D	0.246	6.25	1/4 (0.2500)
E	0.250	6.35	1/4 (0.2500)
F	0.257	6.53	1/4 (0.2500)
G	0.261	6.63	17/64 (0.2656)
H	0.266	6.76	17/64 (0.2656)
I	0.272	6.91	17/64 (0.2656)
J	0.277	7.04	9/32 (0.2813)
K	0.281	7.14	9/32 (0.2813)
L	0.290	7.37	19/64 (0.2969)
M	0.295	7.49	19/64 (0.2969)
N	0.302	7.67	19/64 (0.2969)
O	0.316	8.03	5/16 (0.3125)
P	0.323	8.20	21/64 (0.3281)
Q	0.332	8.43	21/64 (0.3281)
R	0.339	8.61	11/32 (0.3438)
S	0.348	8.84	11/32 (0.3438)
T	0.358	9.09	23/64 (0.3594)
U	0.368	9.35	3/8 (0.3750)
V	0.377	9.58	3/8 (0.3750)
W	0.386	9.80	25/64 (0.3906)
X	0.397	10.08	25/64 (0.3906)
Y	0.404	10.26	13/32 (0.4063)
Z	0.413	10.49	13/32 (0.4063)

Finding the bit for a decimal size

Plans and tap charts often give a size like 0.156 or 0.346 inch. Find the closest decimal in any of the three tables:

• 0.156 in: 5/32 (0.1563) or #22 (0.157).
• 0.201 in: #7 exactly. 13/64 (0.2031) is close enough for most work.
• 0.346 in: S (0.348) or 11/32 (0.3438).
• 0.250 in: 1/4 or letter E. They’re the same bit.

To compare with a metric size, multiply inches by 25.4 or use inches to mm: 0.201 in = 5.11 mm, so a 5.1 mm bit is a fine substitute for a #7. To check every series at once, use the drill size calculator: type any size and find the nearest drill bit for it.

Common uses

Drill	Size (in)	Typical use
#43	0.089	Tap drill for #4-40
#36	0.1065	Tap drill for #6-32
#29	0.136	Tap drill for #8-32
#25	0.1495	Tap drill for #10-24
#21	0.159	Tap drill for #10-32
#7	0.201	Tap drill for 1/4-20; free-fit hole for #10
F	0.257	Tap drill for 5/16-18; close-fit hole for 1/4
I	0.272	Tap drill for 5/16-24
Q	0.332	Tap drill for 3/8-24; free-fit hole for 5/16
R	0.339	Tap drill for 1/8 NPT pipe thread
U	0.368	Tap drill for 7/16-14

The full list is in the tap drill chart.

Identifying an unmarked bit

The size is stamped on the shank of most bits, but it wears off. Measure across the smooth shank (not the flutes) with calipers, or push it through the holes of a drill gauge plate. Without calipers, compare it against a mm ruler at actual size: you’ll get within about 0.1 mm, enough to tell a #7 from a #29.

For fractional and metric bits, see the drill bit size chart.

More DIY charts: tap drill sizes · bolt torque · washer sizes · wire gauge · sheet metal gauge.