Drill Bits

Drill bits are cutting tools used in a hand drill, drill press, or mill to create circular holes.

History and Sizing

Historically, drill bits were produced in sizes corresponding to steel wire gauge sizes (leading to ~20 sized diameters). Numbered-size bits range from size 80 (#80, 0.0135”) to size 1 (#1, 0.288”), with less-common letter sizes covering a range of A (0.234”) to Z (0.413”). These sizes are now less common but still often used in the US, and to a lesser extent the UK.

The decimal gauge sizes and intermediate sizes were later standardized to fractional inches, in 1/64” steps. These sizes are now much more common in the US.

In the rest of the world, drill bits are measured in metric sizes, available in steps of 1/20th of a millimeter below 3mm and in 1/10 steps above.

Materials

Drill bits are available in a number of material choices. The least expensive drill bits are carbon steel, which is generally more suited for soft materials such as wood and plastics (not metal). High Speed Steel (HSS) is adequate for use with aluminum, while titanium is comparable but can take somewhat higher temperatures. Cobalt is extremely hard and can withstand very high temperatures, but can have a shorter lifespan and can more easily break.

For general use, HSS is the most cost effective for aluminum, while for steel and other hard materials cobalt is preferable.

Best Practices

To extend the life of your drill bits, use cutting fluid for deep or frequent (extended) drilling. If necessary, WD-40 can be used as a substitue for cutting fluid with aluminum.

It is very important to use properly-sized drill bits. When drilling a clearance hole, too loose of a hole will lead to sloppy construction (caused by a too-large drill bit), while an undersized hole will be too small for your bolt or other part. When drilling a hole that will be tapped, hole size will determine thread engagement. Typically, look for a hole size that will lead to about 75% thread engagement after tapping.

Standardization of fastening hardware is important for teams to reduce cost, as both fasteners and drill bits can then be bought in bulk. This can also help to reduce the variety of drill bits and other tools necessary to have on hand.

For very accurate hole sizes for bearing and bushings, the hole size should be drilled undersized (~0.008 inch) and completed with a reamer of the final size.

Sizing Tables

The following tables are broken down by standard, followed by a complete reference table for comparison.

Drill Bit Sizes by Fractional Inch

Drill Size	Inches	Millimeters
1/64”	.015625”	.3969 mm
1/32”	.03125”	.7938 mm
3/64”	.046875”	1.1906 mm
1/16”	.0625”	1.5875 mm
5/64”	.078125”	1.9844 mm
3/32”	.09375”	2.3813 mm
7/64”	.109375”	2.7781 mm
1/8”	.125”	3.175 mm
9/64”	.140625”	3.5719 mm
5/32”	.15625”	3.9688 mm
11/64”	.171875”	4.3656 mm
3/16”	.1875”	4.7625 mm
13/64”	.203125”	5.1594 mm
7/32”	.21875”	5.5563 mm
15/64”	.234375”	5.9531 mm
1/4”	.25”	6.35 mm
17/64”	.265625”	6.7469 mm
9/32”	.28125”	7.1438 mm
19/64”	.296875”	7.5406 mm
5/16”	.3125”	7.9375 mm
21/64”	.328125”	8.3344 mm
11/32”	.34375”	8.7313 mm
23/64”	.359375”	9.1281 mm
3/8”	.375”	9.525 mm
25/64”	.390625”	9.9219 mm
13/32”	.40625”	10.3188 mm
27/64”	.421875”	10.7156 mm
7/16”	.4375”	11.1125 mm
29/64”	.453125”	11.5094 mm
15/32”	.46875”	11.9063 mm
31/64”	.484375”	12.3031 mm
1/2”	.5”	12.7 mm
33/64”	.515625”	13.0969 mm
17/32”	.53125”	13.4938 mm
35/64”	.546875”	13.8906 mm
9/16”	.5625”	14.2875 mm
37/64”	.578125”	14.6844 mm
19/32”	.59375”	15.0813 mm
39/64”	.609375”	15.4781 mm
5/8”	.625”	15.875 mm
41/64”	.640625”	16.2719 mm
21/32”	.65625”	16.6688 mm
43/64”	.671875”	17.0656 mm
11/16”	.6875”	17.4625 mm
45/64”	.703125”	17.8594 mm
23/32”	.71875”	18.2563 mm
47/64”	.734375”	18.6531 mm
3/4”	.75”	19.05 mm
49/64”	.765625”	19.4469 mm
25/32”	.78125”	19.8438 mm
51/64”	.796875”	20.2406 mm
13/16”	.8125”	20.6375 mm
53/64”	.828125”	21.0344 mm
27/32”	.84375”	21.4313 mm
55/64”	.859375”	21.8281 mm
7/8”	.875”	22.225 mm
57/64”	.890625”	22.6219 mm
29/32”	.90625”	23.0188 mm
59/64”	.921875”	23.4156 mm
15/16”	.9375”	23.8125 mm
61/64”	.953125”	24.2094 mm
31/32”	.96875”	24.6063 mm
63/64”	.984375”	25.0031 mm
1”	1.000”	25.4 mm

Drill Bit Sizes by Gauge

Drill Size	Inches	Millimeters
#80	.0135”	.3429 mm
#79	.0145”	.3683 mm
#78	.016”	.4064 mm
#77	.018”	.4572 mm
#76	.02”	.508 mm
#75	.021”	.5334 mm
#74	.0225”	.5715 mm
#73	.024”	.6096 mm
#72	.025”	.635 mm
#71	.026”	.6604 mm
#70	.028”	.7112 mm
#69	.0292”	.74168 mm
#68	.031”	.7874 mm
#67	.032”	.8128 mm
#66	.033”	.8382 mm
#65	.035”	.889 mm
#64	.036”	.9144 mm
#63	.037”	.9398 mm
#62	.038”	.9652 mm
#61	.039”	.9906 mm
#60	.04”	1.016 mm
#59	.041”	1.0414 mm
#58	.042”	1.0668 mm
#57	.043”	1.0922 mm
#56	.0465”	1.1811 mm
#55	.052”	1.3208 mm
#54	.055”	1.397 mm
#53	.0595”	1.5113 mm
#52	.0635”	1.6129 mm
#51	.067”	1.7018 mm
#50	.07”	1.778 mm
#49	.073”	1.8542 mm
#48	.076”	1.9304 mm
#47	.0785”	1.9939 mm
#46	.081”	2.0574 mm
#45	.082”	2.0828 mm
#44	.086”	2.1844 mm
#43	.089”	2.2606 mm
#42	.0935”	2.3749 mm
#41	.096”	2.4384 mm
#40	.098”	2.4892 mm
#39	.0995”	2.5273 mm
#38	.1015”	2.5781 mm
#37	.104”	2.6416 mm
#36	.1065”	2.7051 mm
#35	.11”	2.794 mm
#34	.111”	2.8194 mm
#33	.113”	2.8702 mm
#32	.116”	2.9464 mm
#31	.12”	3.048 mm
#30	.1285”	3.2639 mm
#29	.136”	3.4544 mm
#28	.1405”	3.5687 mm
#27	.144”	3.6576 mm
#26	.147”	3.7338 mm
#25	.1495”	3.7973 mm
#24	.152”	3.8608 mm
#23	.154”	3.9116 mm
#22	.157”	3.9878 mm
#21	.159”	4.0386 mm
#20	.161”	4.0894 mm
#19	.166”	4.2164 mm
#18	.1695”	4.3053 mm
#17	.173”	4.3942 mm
#16	.177”	4.4958 mm
#15	.18”	4.572 mm
#14	.182”	4.6228 mm
#13	.185”	4.699 mm
#12	.189”	4.8006 mm
#11	.191”	4.8514 mm
#10	.1935”	4.9149 mm
#9	.196”	4.9784 mm
#8	.199”	5.0546 mm
#7	.201”	5.1054 mm
#6	.204”	5.1816 mm
#5	.2055”	5.2197 mm
#4	.209”	5.3086 mm
#3	.213”	5.4102 mm
#2	.221”	5.6134 mm
#1	.228”	5.7912 mm

Drill Bit Sizes by Letter

Drill Size	Inches	Millimeters
A	.234”	5.9436 mm
B	.238”	6.0452 mm
C	.242”	6.1468 mm
D	.246”	6.2484 mm
E	.25”	6.35 mm
F	.257”	6.5278 mm
G	.261”	6.6294 mm
H	.266”	6.7564 mm
I	.272”	6.9088 mm
J	.277”	7.0358 mm
K	.281”	7.1374 mm
L	.29”	7.366 mm
M	.295”	7.493 mm
N	.302”	7.6708 mm
O	.316”	8.0264 mm
P	.323”	8.2042 mm
Q	.332”	8.4328 mm
R	.339”	8.6106 mm
S	.348”	8.8392 mm
T	.358”	9.0932 mm
U	.368”	9.3472 mm
V	.377”	9.5758 mm
W	.386”	9.8044 mm
X	.397”	10.0838 mm
Y	.404”	10.2616 mm
Z	.413”	10.4902 mm

Metric Drill Bit sizes

Drill Size	Inches	Millimeters
0.5 mm	.0197”	.5 mm
0.75 mm	.0295”	.75 mm
0.85 mm	.0335”	.85 mm
0.95 mm	.0374”	.95 mm
1 mm	.0394”	1 mm
1.1 mm	.0433”	1.1 mm
1.25 mm	.0492”	1.25 mm
1.3 mm	.0512”	1.3 mm
1.45 mm	.0571”	1.45 mm
1.5 mm	.0591”	1.5 mm
1.6 mm	.063”	1.6 mm
1.75 mm	.0689”	1.75 mm
2 mm	.0787”	2 mm
2.05 mm	.0807”	2.05 mm
2.5 mm	.0984”	2.5 mm
2.9 mm	.1142”	2.9 mm
3 mm	.1181”	3 mm
3.3 mm	.1299”	3.3 mm
3.5 mm	.1378”	3.5 mm
3.6 mm	.1417”	3.6 mm
3.7 mm	.1457”	3.7 mm
4 mm	.1575”	4 mm
4.2 mm	.1654”	4.2 mm
4.5 mm	.1772”	4.5 mm
5 mm	.1969”	5 mm
5.25 mm	.2067”	5.25 mm
5.5 mm	.2165”	5.5 mm
6 mm	.2362”	6 mm
6.25 mm	.2461”	6.25 mm
6.5 mm	.2559”	6.5 mm
6.8 mm	.2677”	6.8 mm
7 mm	.2756”	7 mm
7.25 mm	.2854”	7.25 mm
7.5 mm	.2953”	7.5 mm
7.8 mm	.3071”	7.8 mm
8 mm	.315”	8 mm
8.5 mm	.3346”	8.5 mm
8.8 mm	.3465”	8.8 mm
9 mm	.3543”	9 mm
9.25 mm	.3642”	9.25 mm
9.5 mm	.374”	9.5 mm
10 mm	.3937”	10 mm
10.2 mm	.4016”	10.2 mm
10.5 mm	.4134”	10.5 mm
11 mm	.4331”	11 mm
11.25 mm	.4429”	11.25 mm
11.5 mm	.4528”	11.5 mm
12 mm	.4724”	12 mm
12.5 mm	.4921”	12.5 mm
12.8 mm	.5039”	12.8 mm
13 mm	.5118”	13 mm
13.5 mm	.5315”	13.5 mm
14 mm	.5512”	14 mm
14.5 mm	.5709”	14.5 mm
15 mm	.5906”	15 mm
15.5 mm	.6102”	15.5 mm
16 mm	.6299”	16 mm
16.5 mm	.6496”	16.5 mm
17 mm	.6693”	17 mm
17.5 mm	.689”	17.5 mm
18 mm	.7087”	18 mm
18.5 mm	.7283”	18.5 mm
19 mm	.748”	19 mm
19.5 mm	.7677”	19.5 mm
20 mm	.7874”	20 mm
20.5 mm	.8071”	20.5 mm
21 mm	.8268”	21 mm
21.5 mm	.8465”	21.5 mm
22 mm	.8661”	22 mm
22.5 mm	.8858”	22.5 mm
23 mm	.9055”	23 mm
23.5 mm	.9252”	23.5 mm
24 mm	.9449”	24 mm
24.5 mm	.9646”	24.5 mm
25 mm	.9843”	25 mm

Table of Drill Bit Sizes

Drill Size	Inches	Millimeters
#80	.0135”	.3429 mm
#79	.0145”	.3683 mm
1/64”	.015625”	.3969 mm
#78	.016”	.4064 mm
#77	.018”	.4572 mm
0.5 mm	.0197”	.5 mm
#76	.02”	.508 mm
#75	.021”	.5334 mm
#74	.0225”	.5715 mm
#73	.024”	.6096 mm
#72	.025”	.635 mm
#71	.026”	.6604 mm
#70	.028”	.7112 mm
#69	.0292”	.74168 mm
0.75 mm	.0295”	.75 mm
#68	.031”	.7874 mm
1/32”	.03125”	.7938 mm
#67	.032”	.8128 mm
#66	.033”	.8382 mm
0.85 mm	.0335”	.85 mm
#65	.035”	.889 mm
#64	.036”	.9144 mm
#63	.037”	.9398 mm
0.95 mm	.0374”	.95 mm
#62	.038”	.9652 mm
#61	.039”	.9906 mm
1 mm	.0394”	1 mm
#60	.04”	1.016 mm
#59	.041”	1.0414 mm
#58	.042”	1.0668 mm
#57	.043”	1.0922 mm
1.1 mm	.0433”	1.1 mm
#56	.0465”	1.1811 mm
3/64”	.046875”	1.1906 mm
1.25 mm	.0492”	1.25 mm
1.3 mm	.0512”	1.3 mm
#55	.052”	1.3208 mm
#54	.055”	1.397 mm
1.45 mm	.0571”	1.45 mm
1.5 mm	.0591”	1.5 mm
#53	.0595”	1.5113 mm
1/16”	.0625”	1.5875 mm
1.6 mm	.063”	1.6 mm
#52	.0635”	1.6129 mm
#51	.067”	1.7018 mm
1.75 mm	.0689”	1.75 mm
#50	.07”	1.778 mm
#49	.073”	1.8542 mm
#48	.076”	1.9304 mm
5/64”	.078125”	1.9844 mm
#47	.0785”	1.9939 mm
2 mm	.0787”	2 mm
2.05 mm	.0807”	2.05 mm
#46	.081”	2.0574 mm
#45	.082”	2.0828 mm
#44	.086”	2.1844 mm
#43	.089”	2.2606 mm
#42	.0935”	2.3749 mm
3/32”	.09375”	2.3813 mm
#41	.096”	2.4384 mm
#40	.098”	2.4892 mm
2.5 mm	.0984”	2.5 mm
#39	.0995”	2.5273 mm
#38	.1015”	2.5781 mm
#37	.104”	2.6416 mm
#36	.1065”	2.7051 mm
7/64”	.109375”	2.7781 mm
#35	.11”	2.794 mm
#34	.111”	2.8194 mm
#33	.113”	2.8702 mm
2.9 mm	.1142”	2.9 mm
#32	.116”	2.9464 mm
3 mm	.1181”	3 mm
#31	.12”	3.048 mm
1/8”	.125”	3.175 mm
#30	.1285”	3.2639 mm
3.3 mm	.1299”	3.3 mm
#29	.136”	3.4544 mm
3.5 mm	.1378”	3.5 mm
#28	.1405”	3.5687 mm
9/64”	.140625”	3.5719 mm
3.6 mm	.1417”	3.6 mm
#27	.144”	3.6576 mm
3.7 mm	.1457”	3.7 mm
#26	.147”	3.7338 mm
#25	.1495”	3.7973 mm
#24	.152”	3.8608 mm
#23	.154”	3.9116 mm
5/32”	.15625”	3.9688 mm
#22	.157”	3.9878 mm
4 mm	.1575”	4 mm
#21	.159”	4.0386 mm
#20	.161”	4.0894 mm
4.2 mm	.1654”	4.2 mm
#19	.166”	4.2164 mm
#18	.1695”	4.3053 mm
11/64”	.171875”	4.3656 mm
#17	.173”	4.3942 mm
#16	.177”	4.4958 mm
4.5 mm	.1772”	4.5 mm
#15	.18”	4.572 mm
#14	.182”	4.6228 mm
#13	.185”	4.699 mm
3/16”	.1875”	4.7625 mm
#12	.189”	4.8006 mm
#11	.191”	4.8514 mm
#10	.1935”	4.9149 mm
#9	.196”	4.9784 mm
5 mm	.1969”	5 mm
#8	.199”	5.0546 mm
#7	.201”	5.1054 mm
13/64”	.203125”	5.1594 mm
#6	.204”	5.1816 mm
#5	.2055”	5.2197 mm
5.25 mm	.2067”	5.25 mm
#4	.209”	5.3086 mm
#3	.213”	5.4102 mm
5.5 mm	.2165”	5.5 mm
7/32”	.21875”	5.5563 mm
#2	.221”	5.6134 mm
#1	.228”	5.7912 mm
A	.234”	5.9436 mm
15/64”	.234375”	5.9531 mm
6 mm	.2362”	6 mm
B	.238”	6.0452 mm
C	.242”	6.1468 mm
D	.246”	6.2484 mm
6.25 mm	.2461”	6.25 mm
1/4”	.25”	6.35 mm
E	.25”	6.35 mm
6.5 mm	.2559”	6.5 mm
F	.257”	6.5278 mm
G	.261”	6.6294 mm
17/64”	.265625”	6.7469 mm
H	.266”	6.7564 mm
6.8 mm	.2677”	6.8 mm
I	.272”	6.9088 mm
7 mm	.2756”	7 mm
J	.277”	7.0358 mm
K	.281”	7.1374 mm
9/32”	.28125”	7.1438 mm
7.25 mm	.2854”	7.25 mm
L	.29”	7.366 mm
M	.295”	7.493 mm
7.5 mm	.2953”	7.5 mm
19/64”	.296875”	7.5406 mm
N	.302”	7.6708 mm
7.8 mm	.3071”	7.8 mm
5/16”	.3125”	7.9375 mm
8 mm	.315”	8 mm
O	.316”	8.0264 mm
P	.323”	8.2042 mm
21/64”	.328125”	8.3344 mm
Q	.332”	8.4328 mm
8.5 mm	.3346”	8.5 mm
R	.339”	8.6106 mm
11/32”	.34375”	8.7313 mm
8.8 mm	.3465”	8.8 mm
S	.348”	8.8392 mm
9 mm	.3543”	9 mm
T	.358”	9.0932 mm
23/64”	.359375”	9.1281 mm
9.25 mm	.3642”	9.25 mm
U	.368”	9.3472 mm
9.5 mm	.374”	9.5 mm
3/8”	.375”	9.525 mm
V	.377”	9.5758 mm
W	.386”	9.8044 mm
25/64”	.390625”	9.9219 mm
10 mm	.3937”	10 mm
X	.397”	10.0838 mm
10.2 mm	.4016”	10.2 mm
Y	.404”	10.2616 mm
13/32”	.40625”	10.3188 mm
Z	.413”	10.4902 mm
10.5 mm	.4134”	10.5 mm
27/64”	.421875”	10.7156 mm
11 mm	.4331”	11 mm
7/16”	.4375”	11.1125 mm
11.25 mm	.4429”	11.25 mm
11.5 mm	.4528”	11.5 mm
29/64”	.453125”	11.5094 mm
15/32”	.46875”	11.9063 mm
12 mm	.4724”	12 mm
31/64”	.484375”	12.3031 mm
12.5 mm	.4921”	12.5 mm
1/2”	.5”	12.7 mm
12.8 mm	.5039”	12.8 mm
13 mm	.5118”	13 mm
33/64”	.515625”	13.0969 mm
17/32”	.53125”	13.4938 mm
13.5 mm	.5315”	13.5 mm
35/64”	.546875”	13.8906 mm
14 mm	.5512”	14 mm
9/16”	.5625”	14.2875 mm
14.5 mm	.5709”	14.5 mm
37/64”	.578125”	14.6844 mm
15 mm	.5906”	15 mm
19/32”	.59375”	15.0813 mm
39/64”	.609375”	15.4781 mm
15.5 mm	.6102”	15.5 mm
5/8”	.625”	15.875 mm
16 mm	.6299”	16 mm
41/64”	.640625”	16.2719 mm
16.5 mm	.6496”	16.5 mm
21/32”	.65625”	16.6688 mm
17 mm	.6693”	17 mm
43/64”	.671875”	17.0656 mm
11/16”	.6875”	17.4625 mm
17.5 mm	.689”	17.5 mm
45/64”	.703125”	17.8594 mm
18 mm	.7087”	18 mm
23/32”	.71875”	18.2563 mm
18.5 mm	.7283”	18.5 mm
47/64”	.734375”	18.6531 mm
19 mm	.748”	19 mm
3/4”	.75”	19.05 mm
49/64”	.765625”	19.4469 mm
19.5 mm	.7677”	19.5 mm
25/32”	.78125”	19.8438 mm
20 mm	.7874”	20 mm
51/64”	.796875”	20.2406 mm
20.5 mm	.8071”	20.5 mm
13/16”	.8125”	20.6375 mm
21 mm	.8268”	21 mm
53/64”	.828125”	21.0344 mm
27/32”	.84375”	21.4313 mm
21.5 mm	.8465”	21.5 mm
55/64”	.859375”	21.8281 mm
22 mm	.8661”	22 mm
7/8”	.875”	22.225 mm
22.5 mm	.8858”	22.5 mm
57/64”	.890625”	22.6219 mm
23 mm	.9055”	23 mm
29/32”	.90625”	23.0188 mm
59/64”	.921875”	23.4156 mm
23.5 mm	.9252”	23.5 mm
15/16”	.9375”	23.8125 mm
24 mm	.9449”	24 mm
61/64”	.953125”	24.2094 mm
24.5 mm	.9646”	24.5 mm
31/32”	.96875”	24.6063 mm
25 mm	.9843”	25 mm
63/64”	.984375”	25.0031 mm
1”	1.000”	25.4 mm