Drill Bit Size Chart: Number, Letter, Fraction, mm

Twist drills come in four series: fractional inch sizes in steps of 1/64 in, number sizes from #80 (the smallest) to #1, letter sizes from A to Z, and metric sizes in millimetres. The number and letter sizes fill the gaps between fractions, which is why tap drill charts call for drills such as #7 or F. This chart puts all four series in one list sorted by diameter, with decimal inch and millimetre values, so you can find the nearest drill you own to any size. Type a size in the box to filter, or click a heading to sort.

Drill bit size chart: number, letter, fractional and metric

Find a size

Drill	Series	Diameter (in)	Diameter (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
0.5 mm	metric	0.0197	0.50
#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	0.0312	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
#43	number	0.0890	2.26
#42	number	0.0935	2.37
3/32"	fractional	0.0938	2.38
#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
#30	number	0.1285	3.26
#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	0.1562	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
#19	number	0.1660	4.22
#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
#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
#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
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
6.5 mm	metric	0.2559	6.50
F	letter	0.2570	6.53
G	letter	0.2610	6.63
17/64"	fractional	0.2656	6.75
H	letter	0.2660	6.76
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	0.2812	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
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
Y	letter	0.4040	10.26
13/32"	fractional	0.4062	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	0.5312	13.49
35/64"	fractional	0.5469	13.89
9/16"	fractional	0.5625	14.29
37/64"	fractional	0.5781	14.68
19/32"	fractional	0.5938	15.08
39/64"	fractional	0.6094	15.48
5/8"	fractional	0.6250	15.88
41/64"	fractional	0.6406	16.27
21/32"	fractional	0.6562	16.67
43/64"	fractional	0.6719	17.07
11/16"	fractional	0.6875	17.46
45/64"	fractional	0.7031	17.86
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	0.7812	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	0.9062	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

Number and letter drill diameters from the ASME B94.11M twist drill series (the list our tap drill calculator uses); fractional sizes are exact 64ths of an inch and metric sizes exact millimetres (0.5 to 13 mm in 0.5 mm steps). Conversions: 1 in = 25.4 mm, our arithmetic.

How the series fit together

Number drills run backwards: #80 is 0.0135 in and #1 is 0.2280 in. A #29 drill is 0.1360 in, the tap drill for 8-32 screws; a #7 is 0.2010 in, the tap drill for 1/4-20.
Letter drills carry on where the numbers stop: A is 0.234 in, just over #1, and Z is 0.413 in.
Fractional drills in a standard index go from 1/16 to 1/2 in by 64ths; larger sets add 1/32 steps.
Metric drills commonly come in 0.5 mm steps, with 0.1 mm steps in jobber sets for tapping.

Finding a substitute

Sort the table by diameter and look at the sizes next to the one you need. A 13/64 in drill (0.2031 in) is 0.0021 in larger than a #7 (0.2010 in), close enough for tapping 1/4-20 in most materials. A 6.5 mm drill (0.2559 in) sits between 1/4 in and F (0.2570 in). For tapping, choose with the tap drill chart, which shows the thread percentage each drill gives; for bolts that must pass through, use the clearance hole chart; for wood screws, the wood screw size chart lists pilot and clearance holes.

Practical notes

Drills cut slightly oversize, typically by a few thousandths of an inch, more with a worn or poorly sharpened point; measure the hole, not the drill, when fit matters.
Drill gauges and the shank markings on most bits show the size; small number drills are usually marked only on the case, so keep them in an indexed box.
For holes over about 1/2 in in metal, drill a pilot first; in wood, brad-point and Forstner bits give cleaner holes than twist drills.

Frequently asked questions

What size is a #7 drill bit?

0.2010 in (5.11 mm), the tap drill for 1/4-20 UNC.

What is the decimal size of a letter F drill?

0.2570 in (6.53 mm), the usual tap drill for 5/16-18.

What drill bit is closest to 5 mm?

#9 (0.1960 in = 4.98 mm) and #8 (0.1990 in = 5.05 mm) are the nearest; 13/64 in is 5.16 mm.

Which is bigger, a #1 or a #80 drill?

#1 is the biggest number drill (0.228 in); #80 is the smallest (0.0135 in).

Sources and method

Number and letter sizes are the standard decimal equivalents; fractional and metric rows are exact. The list is sorted by diameter so neighbouring sizes are substitutes.

ASME B94.11M, Twist Drills: number and letter drill diameters (as used by our tap drill calculator).
Fractional and metric sizes and conversions: exact values, our arithmetic.

More thread and fastener tools

Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.