What order do number drill sizes go in?

Backwards, like wire gauge. Number 1 is the largest at 0.228 inches and number 80 is the smallest at 0.0135 inches. Letter sizes run the other way: A is the smallest at 0.234 inches and Z the largest at 0.413 inches.

What is the metric equivalent of a 1/4 inch drill?

A quarter inch is 6.35 mm exactly. The nearest common metric drills are 6.5 mm, which is 0.2559 inches and slightly oversize, and 6.0 mm, which is 0.2362 inches and undersize. There is no exact metric equivalent.

Gauge Charts

Drill Bit Size Chart

Twist drills come in four overlapping series, and a full index contains all of them because the gaps in any one series are too coarse for close work. Fractional sizes step by 1/64 inch, number sizes fill the range from 0.0135 up to 0.228 inches, letter sizes carry on from 0.234 to 0.413 inches, and metric drills interleave with all three.

Drill size finder

252 sizes, ANSI/ASME B94.11M

Size	Series	Inches	mm
#80	Number	0.0135	0.34
#79	Number	0.0145	0.37
1/64	Fractional	0.0156	0.40
#78	Number	0.0160	0.41
#77	Number	0.0180	0.46
#76	Number	0.0200	0.51
#75	Number	0.0210	0.53
#74	Number	0.0225	0.57
#73	Number	0.0240	0.61
#72	Number	0.0250	0.64
#71	Number	0.0260	0.66
#70	Number	0.0280	0.71
#69	Number	0.0292	0.74
#68	Number	0.0310	0.79
1/32	Fractional	0.0313	0.79
#67	Number	0.0320	0.81
#66	Number	0.0330	0.84
#65	Number	0.0350	0.89
#64	Number	0.0360	0.91
#63	Number	0.0370	0.94
#62	Number	0.0380	0.97
#61	Number	0.0390	0.99
1 mm	Metric	0.0394	1.00
#60	Number	0.0400	1.02
#59	Number	0.0410	1.04
#58	Number	0.0420	1.07
#57	Number	0.0430	1.09
#56	Number	0.0465	1.18
3/64	Fractional	0.0469	1.19
#55	Number	0.0520	1.32
#54	Number	0.0550	1.40
1.5 mm	Metric	0.0591	1.50
#53	Number	0.0595	1.51
1/16	Fractional	0.0625	1.59
#52	Number	0.0635	1.61
#51	Number	0.0670	1.70
#50	Number	0.0700	1.78
#49	Number	0.0730	1.85
#48	Number	0.0760	1.93
5/64	Fractional	0.0781	1.98
#47	Number	0.0785	1.99
2 mm	Metric	0.0787	2.00
#46	Number	0.0810	2.06
#45	Number	0.0820	2.08
#44	Number	0.0860	2.18
2.2 mm	Metric	0.0866	2.20
#43	Number	0.0890	2.26
#42	Number	0.0935	2.37
3/32	Fractional	0.0938	2.38
2.4 mm	Metric	0.0945	2.40
#41	Number	0.0960	2.44
#40	Number	0.0980	2.49
2.5 mm	Metric	0.0984	2.50
#39	Number	0.0995	2.53
#38	Number	0.1015	2.58
#37	Number	0.1040	2.64
#36	Number	0.1065	2.71
7/64	Fractional	0.1094	2.78
#35	Number	0.1100	2.79
#34	Number	0.1110	2.82
#33	Number	0.1130	2.87
#32	Number	0.1160	2.95
3 mm	Metric	0.1181	3.00
#31	Number	0.1200	3.05
1/8	Fractional	0.1250	3.17
3.2 mm	Metric	0.1260	3.20
#30	Number	0.1285	3.26
3.3 mm	Metric	0.1299	3.30
3.4 mm	Metric	0.1339	3.40
#29	Number	0.1360	3.45
3.5 mm	Metric	0.1378	3.50
#28	Number	0.1405	3.57
9/64	Fractional	0.1406	3.57
#27	Number	0.1440	3.66
#26	Number	0.1470	3.73
#25	Number	0.1495	3.80
#24	Number	0.1520	3.86
#23	Number	0.1540	3.91
5/32	Fractional	0.1563	3.97
#22	Number	0.1570	3.99
4 mm	Metric	0.1575	4.00
#21	Number	0.1590	4.04
#20	Number	0.1610	4.09
4.2 mm	Metric	0.1654	4.20
#19	Number	0.1660	4.22
4.3 mm	Metric	0.1693	4.30
#18	Number	0.1695	4.31
11/64	Fractional	0.1719	4.37
#17	Number	0.1730	4.39
#16	Number	0.1770	4.50
4.5 mm	Metric	0.1772	4.50
#15	Number	0.1800	4.57
#14	Number	0.1820	4.62
#13	Number	0.1850	4.70
3/16	Fractional	0.1875	4.76
4.8 mm	Metric	0.1890	4.80
#12	Number	0.1890	4.80
#11	Number	0.1910	4.85
#10	Number	0.1935	4.91
#9	Number	0.1960	4.98
5 mm	Metric	0.1969	5.00
#8	Number	0.1990	5.05
#7	Number	0.2010	5.11
13/64	Fractional	0.2031	5.16
#6	Number	0.2040	5.18
#5	Number	0.2055	5.22
5.3 mm	Metric	0.2087	5.30
#4	Number	0.2090	5.31
#3	Number	0.2130	5.41
5.5 mm	Metric	0.2165	5.50
7/32	Fractional	0.2188	5.56
#2	Number	0.2210	5.61
#1	Number	0.2280	5.79
5.8 mm	Metric	0.2283	5.80
A	Letter	0.2340	5.94
15/64	Fractional	0.2344	5.95
6 mm	Metric	0.2362	6.00
B	Letter	0.2380	6.05
C	Letter	0.2420	6.15
D	Letter	0.2460	6.25
1/4	Fractional	0.2500	6.35
E	Letter	0.2500	6.35
6.4 mm	Metric	0.2520	6.40
6.5 mm	Metric	0.2559	6.50
F	Letter	0.2570	6.53
6.6 mm	Metric	0.2598	6.60
G	Letter	0.2610	6.63
17/64	Fractional	0.2656	6.75
H	Letter	0.2660	6.76
6.8 mm	Metric	0.2677	6.80
I	Letter	0.2720	6.91
7 mm	Metric	0.2756	7.00
J	Letter	0.2770	7.04
K	Letter	0.2810	7.14
9/32	Fractional	0.2813	7.14
L	Letter	0.2900	7.37
M	Letter	0.2950	7.49
7.5 mm	Metric	0.2953	7.50
19/64	Fractional	0.2969	7.54
N	Letter	0.3020	7.67
5/16	Fractional	0.3125	7.94
8 mm	Metric	0.3150	8.00
O	Letter	0.3160	8.03
P	Letter	0.3230	8.20
21/64	Fractional	0.3281	8.33
8.4 mm	Metric	0.3307	8.40
Q	Letter	0.3320	8.43
8.5 mm	Metric	0.3346	8.50
R	Letter	0.3390	8.61
11/32	Fractional	0.3438	8.73
S	Letter	0.3480	8.84
9 mm	Metric	0.3543	9.00
T	Letter	0.3580	9.09
23/64	Fractional	0.3594	9.13
U	Letter	0.3680	9.35
9.5 mm	Metric	0.3740	9.50
3/8	Fractional	0.3750	9.52
V	Letter	0.3770	9.58
W	Letter	0.3860	9.80
25/64	Fractional	0.3906	9.92
10 mm	Metric	0.3937	10.00
X	Letter	0.3970	10.08
10.2 mm	Metric	0.4016	10.20
Y	Letter	0.4040	10.26
13/32	Fractional	0.4063	10.32
Z	Letter	0.4130	10.49
10.5 mm	Metric	0.4134	10.50
27/64	Fractional	0.4219	10.72
11 mm	Metric	0.4331	11.00
7/16	Fractional	0.4375	11.11
11.5 mm	Metric	0.4528	11.50
29/64	Fractional	0.4531	11.51
15/32	Fractional	0.4688	11.91
12 mm	Metric	0.4724	12.00
31/64	Fractional	0.4844	12.30
12.5 mm	Metric	0.4921	12.50
1/2	Fractional	0.5000	12.70
13 mm	Metric	0.5118	13.00
33/64	Fractional	0.5156	13.10
17/32	Fractional	0.5313	13.49
13.5 mm	Metric	0.5315	13.50
35/64	Fractional	0.5469	13.89
14 mm	Metric	0.5512	14.00
9/16	Fractional	0.5625	14.29
14.5 mm	Metric	0.5709	14.50
37/64	Fractional	0.5781	14.68
15 mm	Metric	0.5906	15.00
19/32	Fractional	0.5938	15.08
39/64	Fractional	0.6094	15.48
15.5 mm	Metric	0.6102	15.50
5/8	Fractional	0.6250	15.88
16 mm	Metric	0.6299	16.00
41/64	Fractional	0.6406	16.27
16.5 mm	Metric	0.6496	16.50
21/32	Fractional	0.6563	16.67
17 mm	Metric	0.6693	17.00
43/64	Fractional	0.6719	17.07
11/16	Fractional	0.6875	17.46
17.5 mm	Metric	0.6890	17.50
45/64	Fractional	0.7031	17.86
18 mm	Metric	0.7087	18.00
23/32	Fractional	0.7188	18.26
47/64	Fractional	0.7344	18.65
3/4	Fractional	0.7500	19.05
49/64	Fractional	0.7656	19.45
25/32	Fractional	0.7813	19.84
51/64	Fractional	0.7969	20.24
13/16	Fractional	0.8125	20.64
53/64	Fractional	0.8281	21.03
27/32	Fractional	0.8438	21.43
55/64	Fractional	0.8594	21.83
7/8	Fractional	0.8750	22.22
57/64	Fractional	0.8906	22.62
29/32	Fractional	0.9063	23.02
59/64	Fractional	0.9219	23.42
15/16	Fractional	0.9375	23.81
61/64	Fractional	0.9531	24.21
31/32	Fractional	0.9688	24.61
63/64	Fractional	0.9844	25.00
1	Fractional	1.0000	25.40
1-1/64	Fractional	1.0156	25.80
1-1/32	Fractional	1.0313	26.19
1-3/64	Fractional	1.0469	26.59
1-1/16	Fractional	1.0625	26.99
1-5/64	Fractional	1.0781	27.38
1-3/32	Fractional	1.0938	27.78
1-7/64	Fractional	1.1094	28.18
1-1/8	Fractional	1.1250	28.57
1-9/64	Fractional	1.1406	28.97
1-5/32	Fractional	1.1563	29.37
1-11/64	Fractional	1.1719	29.77
1-3/16	Fractional	1.1875	30.16
1-13/64	Fractional	1.2031	30.56
1-7/32	Fractional	1.2188	30.96
1-15/64	Fractional	1.2344	31.35
1-1/4	Fractional	1.2500	31.75
1-17/64	Fractional	1.2656	32.15
1-9/32	Fractional	1.2813	32.54
1-19/64	Fractional	1.2969	32.94
1-5/16	Fractional	1.3125	33.34
1-21/64	Fractional	1.3281	33.73
1-11/32	Fractional	1.3438	34.13
1-23/64	Fractional	1.3594	34.53
1-3/8	Fractional	1.3750	34.92
1-25/64	Fractional	1.3906	35.32
1-13/32	Fractional	1.4063	35.72
1-27/64	Fractional	1.4219	36.12
1-7/16	Fractional	1.4375	36.51
1-29/64	Fractional	1.4531	36.91
1-15/32	Fractional	1.4688	37.31
1-31/64	Fractional	1.4844	37.70
1-1/2	Fractional	1.5000	38.10

Inch and metric use different conventions, and most charts hide it. Inch tap drills target about 75% thread, which holds roughly 95% of the strength of a full-depth thread while cutting tapping torque sharply. The metric rule is “subtract the pitch”, so M6 × 1.0 takes a 5.0 mm drill, and that lands at about 92%. Both are the stocked standard. The % thread column shows what the listed drill actually gives; amber marks anything above 85%, where tapping torque climbs and taps break in hard material. Use the slider to size a drill for a different engagement.

All drill sizes by diameter

Sorted by actual diameter so the next size up or down is always the next row, whichever series it belongs to. Fractional sizes are exact by definition; number and letter decimals are the ANSI standard values.

Drill sizes: fractional, number, letter and metric, sorted by diameter
Size	Series	Inches	mm
#80	Number	0.0135	0.34
#79	Number	0.0145	0.37
1/64	Fractional	0.0156	0.40
#78	Number	0.0160	0.41
#77	Number	0.0180	0.46
#76	Number	0.0200	0.51
#75	Number	0.0210	0.53
#74	Number	0.0225	0.57
#73	Number	0.0240	0.61
#72	Number	0.0250	0.64
#71	Number	0.0260	0.66
#70	Number	0.0280	0.71
#69	Number	0.0292	0.74
#68	Number	0.0310	0.79
1/32	Fractional	0.0313	0.79
#67	Number	0.0320	0.81
#66	Number	0.0330	0.84
#65	Number	0.0350	0.89
#64	Number	0.0360	0.91
#63	Number	0.0370	0.94
#62	Number	0.0380	0.97
#61	Number	0.0390	0.99
1 mm	Metric	0.0394	1.00
#60	Number	0.0400	1.02
#59	Number	0.0410	1.04
#58	Number	0.0420	1.07
#57	Number	0.0430	1.09
#56	Number	0.0465	1.18
3/64	Fractional	0.0469	1.19
#55	Number	0.0520	1.32
#54	Number	0.0550	1.40
1.5 mm	Metric	0.0591	1.50
#53	Number	0.0595	1.51
1/16	Fractional	0.0625	1.59
#52	Number	0.0635	1.61
#51	Number	0.0670	1.70
#50	Number	0.0700	1.78
#49	Number	0.0730	1.85
#48	Number	0.0760	1.93
5/64	Fractional	0.0781	1.98
#47	Number	0.0785	1.99
2 mm	Metric	0.0787	2.00
#46	Number	0.0810	2.06
#45	Number	0.0820	2.08
#44	Number	0.0860	2.18
2.2 mm	Metric	0.0866	2.20
#43	Number	0.0890	2.26
#42	Number	0.0935	2.37
3/32	Fractional	0.0938	2.38
2.4 mm	Metric	0.0945	2.40
#41	Number	0.0960	2.44
#40	Number	0.0980	2.49
2.5 mm	Metric	0.0984	2.50
#39	Number	0.0995	2.53
#38	Number	0.1015	2.58
#37	Number	0.1040	2.64
#36	Number	0.1065	2.71
7/64	Fractional	0.1094	2.78
#35	Number	0.1100	2.79
#34	Number	0.1110	2.82
#33	Number	0.1130	2.87
#32	Number	0.1160	2.95
3 mm	Metric	0.1181	3.00
#31	Number	0.1200	3.05
1/8	Fractional	0.1250	3.17
3.2 mm	Metric	0.1260	3.20
#30	Number	0.1285	3.26
3.3 mm	Metric	0.1299	3.30
3.4 mm	Metric	0.1339	3.40
#29	Number	0.1360	3.45
3.5 mm	Metric	0.1378	3.50
#28	Number	0.1405	3.57
9/64	Fractional	0.1406	3.57
#27	Number	0.1440	3.66
#26	Number	0.1470	3.73
#25	Number	0.1495	3.80
#24	Number	0.1520	3.86
#23	Number	0.1540	3.91
5/32	Fractional	0.1563	3.97
#22	Number	0.1570	3.99
4 mm	Metric	0.1575	4.00
#21	Number	0.1590	4.04
#20	Number	0.1610	4.09
4.2 mm	Metric	0.1654	4.20
#19	Number	0.1660	4.22
4.3 mm	Metric	0.1693	4.30
#18	Number	0.1695	4.31
11/64	Fractional	0.1719	4.37
#17	Number	0.1730	4.39
#16	Number	0.1770	4.50
4.5 mm	Metric	0.1772	4.50
#15	Number	0.1800	4.57
#14	Number	0.1820	4.62
#13	Number	0.1850	4.70
3/16	Fractional	0.1875	4.76
4.8 mm	Metric	0.1890	4.80
#12	Number	0.1890	4.80
#11	Number	0.1910	4.85
#10	Number	0.1935	4.91
#9	Number	0.1960	4.98
5 mm	Metric	0.1969	5.00
#8	Number	0.1990	5.05
#7	Number	0.2010	5.11
13/64	Fractional	0.2031	5.16
#6	Number	0.2040	5.18
#5	Number	0.2055	5.22
5.3 mm	Metric	0.2087	5.30
#4	Number	0.2090	5.31
#3	Number	0.2130	5.41
5.5 mm	Metric	0.2165	5.50
7/32	Fractional	0.2188	5.56
#2	Number	0.2210	5.61
#1	Number	0.2280	5.79
5.8 mm	Metric	0.2283	5.80
A	Letter	0.2340	5.94
15/64	Fractional	0.2344	5.95
6 mm	Metric	0.2362	6.00
B	Letter	0.2380	6.05
C	Letter	0.2420	6.15
D	Letter	0.2460	6.25
1/4	Fractional	0.2500	6.35
E	Letter	0.2500	6.35
6.4 mm	Metric	0.2520	6.40
6.5 mm	Metric	0.2559	6.50
F	Letter	0.2570	6.53
6.6 mm	Metric	0.2598	6.60
G	Letter	0.2610	6.63
17/64	Fractional	0.2656	6.75
H	Letter	0.2660	6.76
6.8 mm	Metric	0.2677	6.80
I	Letter	0.2720	6.91
7 mm	Metric	0.2756	7.00
J	Letter	0.2770	7.04
K	Letter	0.2810	7.14
9/32	Fractional	0.2813	7.14
L	Letter	0.2900	7.37
M	Letter	0.2950	7.49
7.5 mm	Metric	0.2953	7.50
19/64	Fractional	0.2969	7.54
N	Letter	0.3020	7.67
5/16	Fractional	0.3125	7.94
8 mm	Metric	0.3150	8.00
O	Letter	0.3160	8.03
P	Letter	0.3230	8.20
21/64	Fractional	0.3281	8.33
8.4 mm	Metric	0.3307	8.40
Q	Letter	0.3320	8.43
8.5 mm	Metric	0.3346	8.50
R	Letter	0.3390	8.61
11/32	Fractional	0.3438	8.73
S	Letter	0.3480	8.84
9 mm	Metric	0.3543	9.00
T	Letter	0.3580	9.09
23/64	Fractional	0.3594	9.13
U	Letter	0.3680	9.35
9.5 mm	Metric	0.3740	9.50
3/8	Fractional	0.3750	9.52
V	Letter	0.3770	9.58
W	Letter	0.3860	9.80
25/64	Fractional	0.3906	9.92
10 mm	Metric	0.3937	10.00
X	Letter	0.3970	10.08
10.2 mm	Metric	0.4016	10.20
Y	Letter	0.4040	10.26
13/32	Fractional	0.4063	10.32
Z	Letter	0.4130	10.49
10.5 mm	Metric	0.4134	10.50
27/64	Fractional	0.4219	10.72
11 mm	Metric	0.4331	11.00
7/16	Fractional	0.4375	11.11
11.5 mm	Metric	0.4528	11.50
29/64	Fractional	0.4531	11.51
15/32	Fractional	0.4688	11.91
12 mm	Metric	0.4724	12.00
31/64	Fractional	0.4844	12.30
12.5 mm	Metric	0.4921	12.50
1/2	Fractional	0.5000	12.70
13 mm	Metric	0.5118	13.00
33/64	Fractional	0.5156	13.10
17/32	Fractional	0.5313	13.49
13.5 mm	Metric	0.5315	13.50
35/64	Fractional	0.5469	13.89
14 mm	Metric	0.5512	14.00
9/16	Fractional	0.5625	14.29
14.5 mm	Metric	0.5709	14.50
37/64	Fractional	0.5781	14.68
15 mm	Metric	0.5906	15.00
19/32	Fractional	0.5938	15.08
39/64	Fractional	0.6094	15.48
15.5 mm	Metric	0.6102	15.50
5/8	Fractional	0.6250	15.88
16 mm	Metric	0.6299	16.00
41/64	Fractional	0.6406	16.27
16.5 mm	Metric	0.6496	16.50
21/32	Fractional	0.6563	16.67
17 mm	Metric	0.6693	17.00
43/64	Fractional	0.6719	17.07
11/16	Fractional	0.6875	17.46
17.5 mm	Metric	0.6890	17.50
45/64	Fractional	0.7031	17.86
18 mm	Metric	0.7087	18.00
23/32	Fractional	0.7188	18.26
47/64	Fractional	0.7344	18.65
3/4	Fractional	0.7500	19.05
49/64	Fractional	0.7656	19.45
25/32	Fractional	0.7813	19.84
51/64	Fractional	0.7969	20.24
13/16	Fractional	0.8125	20.64
53/64	Fractional	0.8281	21.03
27/32	Fractional	0.8438	21.43
55/64	Fractional	0.8594	21.83
7/8	Fractional	0.8750	22.22
57/64	Fractional	0.8906	22.62
29/32	Fractional	0.9063	23.02
59/64	Fractional	0.9219	23.42
15/16	Fractional	0.9375	23.81
61/64	Fractional	0.9531	24.21
31/32	Fractional	0.9688	24.61
63/64	Fractional	0.9844	25.00
1	Fractional	1.0000	25.40
1-1/64	Fractional	1.0156	25.80
1-1/32	Fractional	1.0313	26.19
1-3/64	Fractional	1.0469	26.59
1-1/16	Fractional	1.0625	26.99
1-5/64	Fractional	1.0781	27.38
1-3/32	Fractional	1.0938	27.78
1-7/64	Fractional	1.1094	28.18
1-1/8	Fractional	1.1250	28.57
1-9/64	Fractional	1.1406	28.97
1-5/32	Fractional	1.1563	29.37
1-11/64	Fractional	1.1719	29.77
1-3/16	Fractional	1.1875	30.16
1-13/64	Fractional	1.2031	30.56
1-7/32	Fractional	1.2188	30.96
1-15/64	Fractional	1.2344	31.35
1-1/4	Fractional	1.2500	31.75
1-17/64	Fractional	1.2656	32.15
1-9/32	Fractional	1.2813	32.54
1-19/64	Fractional	1.2969	32.94
1-5/16	Fractional	1.3125	33.34
1-21/64	Fractional	1.3281	33.73
1-11/32	Fractional	1.3438	34.13
1-23/64	Fractional	1.3594	34.53
1-3/8	Fractional	1.3750	34.92
1-25/64	Fractional	1.3906	35.32
1-13/32	Fractional	1.4063	35.72
1-27/64	Fractional	1.4219	36.12
1-7/16	Fractional	1.4375	36.51
1-29/64	Fractional	1.4531	36.91
1-15/32	Fractional	1.4688	37.31
1-31/64	Fractional	1.4844	37.70
1-1/2	Fractional	1.5000	38.10

Common questions

What order do number drill sizes go in?: Backwards, like wire gauge. Number 1 is the largest at 0.228 inches and number 80 is the smallest at 0.0135 inches. Letter sizes run the other way: A is the smallest at 0.234 inches and Z the largest at 0.413 inches.
What is the metric equivalent of a 1/4 inch drill?: A quarter inch is 6.35 mm exactly. The nearest common metric drills are 6.5 mm, which is 0.2559 inches and slightly oversize, and 6.0 mm, which is 0.2362 inches and undersize. There is no exact metric equivalent.

Open the gauge chart