Holemaking and tapping

Drill size chart

Number, letter, fractional and metric twist drills sorted by decimal size, in and mm side by side. A #7 drill is 0.2010 in (5.11 mm).

Technical review pending. Formulas and values are cited. This notice comes down after a machinist review.

Source: ANSI/ASME B94.11M (twist drills). Metric conversions at 25.4 mm per inch.

Drill sizes sorted by decimal inch: number, letter, fractional and metric
Drill	Type	Decimal (in)	Metric (mm)
#80	Number	0.0135	0.343
#79	Number	0.0145	0.368
1/64	Fraction	0.0156	0.397
#78	Number	0.0160	0.406
#77	Number	0.0180	0.457
0.5 mm	Metric	0.0197	0.500
#76	Number	0.0200	0.508
#75	Number	0.0210	0.533
#74	Number	0.0225	0.572
#73	Number	0.0240	0.610
#72	Number	0.0250	0.635
#71	Number	0.0260	0.660
#70	Number	0.0280	0.711
#69	Number	0.0292	0.742
#68	Number	0.0310	0.787
1/32	Fraction	0.0313	0.794
#67	Number	0.0320	0.813
#66	Number	0.0330	0.838
#65	Number	0.0350	0.889
#64	Number	0.0360	0.914
#63	Number	0.0370	0.940
#62	Number	0.0380	0.965
#61	Number	0.0390	0.991
1.0 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	Fraction	0.0469	1.19
1.25 mm	Metric	0.0492	1.25
#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	Fraction	0.0625	1.59
1.6 mm	Metric	0.0630	1.60
#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	Fraction	0.0781	1.98
#47	Number	0.0785	1.99
2.0 mm	Metric	0.0787	2.00
2.05 mm	Metric	0.0807	2.05
#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	Fraction	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	Fraction	0.1094	2.78
#35	Number	0.1100	2.79
#34	Number	0.1110	2.82
#33	Number	0.1130	2.87
2.9 mm	Metric	0.1142	2.90
#32	Number	0.1160	2.95
3.0 mm	Metric	0.1181	3.00
#31	Number	0.1200	3.05
1/8	Fraction	0.1250	3.18
#30	Number	0.1285	3.26
3.3 mm	Metric	0.1299	3.30
#29	Number	0.1360	3.45
3.5 mm	Metric	0.1378	3.50
#28	Number	0.1405	3.57
9/64	Fraction	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	Fraction	0.1563	3.97
#22	Number	0.1570	3.99
4.0 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
#18	Number	0.1695	4.31
11/64	Fraction	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	Fraction	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
5.0 mm	Metric	0.1969	5.00
#8	Number	0.1990	5.05
#7	Number	0.2010	5.11
13/64	Fraction	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	Fraction	0.2188	5.56
#2	Number	0.2210	5.61
#1	Number	0.2280	5.79
A	Letter	0.2340	5.94
15/64	Fraction	0.2344	5.95
6.0 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	Fraction	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	Fraction	0.2656	6.75
H	Letter	0.2660	6.76
6.8 mm	Metric	0.2677	6.80
I	Letter	0.2720	6.91
7.0 mm	Metric	0.2756	7.00
J	Letter	0.2770	7.04
K	Letter	0.2810	7.14
9/32	Fraction	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	Fraction	0.2969	7.54
N	Letter	0.3020	7.67
5/16	Fraction	0.3125	7.94
8.0 mm	Metric	0.3150	8.00
O	Letter	0.3160	8.03
P	Letter	0.3230	8.20
21/64	Fraction	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	Fraction	0.3438	8.73
8.8 mm	Metric	0.3465	8.80
S	Letter	0.3480	8.84
9.0 mm	Metric	0.3543	9.00
T	Letter	0.3580	9.09
23/64	Fraction	0.3594	9.13
U	Letter	0.3680	9.35
9.5 mm	Metric	0.3740	9.50
3/8	Fraction	0.3750	9.53
V	Letter	0.3770	9.58
W	Letter	0.3860	9.80
25/64	Fraction	0.3906	9.92
10.0 mm	Metric	0.3937	10.00
X	Letter	0.3970	10.08
Y	Letter	0.4040	10.26
10.3 mm	Metric	0.4055	10.30
13/32	Fraction	0.4063	10.32
Z	Letter	0.4130	10.49
10.5 mm	Metric	0.4134	10.50
27/64	Fraction	0.4219	10.72
10.8 mm	Metric	0.4252	10.80
11.0 mm	Metric	0.4331	11.00
7/16	Fraction	0.4375	11.11
11.5 mm	Metric	0.4528	11.50
29/64	Fraction	0.4531	11.51
15/32	Fraction	0.4688	11.91
12.0 mm	Metric	0.4724	12.00
12.1 mm	Metric	0.4764	12.10
31/64	Fraction	0.4844	12.30
12.5 mm	Metric	0.4921	12.50
1/2	Fraction	0.5000	12.70
13.0 mm	Metric	0.5118	13.00
33/64	Fraction	0.5156	13.10
17/32	Fraction	0.5313	13.49
35/64	Fraction	0.5469	13.89
14.0 mm	Metric	0.5512	14.00
14.1 mm	Metric	0.5551	14.10
9/16	Fraction	0.5625	14.29
14.5 mm	Metric	0.5709	14.50
37/64	Fraction	0.5781	14.68
19/32	Fraction	0.5938	15.08
39/64	Fraction	0.6094	15.48
15.5 mm	Metric	0.6102	15.50
15.6 mm	Metric	0.6142	15.60
5/8	Fraction	0.6250	15.88
41/64	Fraction	0.6406	16.27
16.5 mm	Metric	0.6496	16.50
21/32	Fraction	0.6563	16.67
43/64	Fraction	0.6719	17.07
11/16	Fraction	0.6875	17.46
17.5 mm	Metric	0.6890	17.50
17.6 mm	Metric	0.6929	17.60
45/64	Fraction	0.7031	17.86
23/32	Fraction	0.7188	18.26
18.5 mm	Metric	0.7283	18.50
47/64	Fraction	0.7344	18.65
3/4	Fraction	0.7500	19.05
49/64	Fraction	0.7656	19.45
19.5 mm	Metric	0.7677	19.50
19.6 mm	Metric	0.7717	19.60
25/32	Fraction	0.7813	19.84
51/64	Fraction	0.7969	20.24
20.5 mm	Metric	0.8071	20.50
13/16	Fraction	0.8125	20.64
21.0 mm	Metric	0.8268	21.00
53/64	Fraction	0.8281	21.03
21.1 mm	Metric	0.8307	21.10
27/32	Fraction	0.8438	21.43
55/64	Fraction	0.8594	21.83
22.0 mm	Metric	0.8661	22.00
22.1 mm	Metric	0.8701	22.10
7/8	Fraction	0.8750	22.23
57/64	Fraction	0.8906	22.62
29/32	Fraction	0.9063	23.02
59/64	Fraction	0.9219	23.42
15/16	Fraction	0.9375	23.81
61/64	Fraction	0.9531	24.21
31/32	Fraction	0.9688	24.61
63/64	Fraction	0.9844	25.00
1	Fraction	1.0000	25.40

Decimal inch to 4 places; fractional sizes are n / 64 rounded to 4 places. Millimeters are inch x 25.4, to 2 places (3 below 1 mm). Metric drills show their nominal mm size and the inch equivalent.

How to read the table

Every drill sits in size order, so the rows above and below any drill are the next sizes you can reach for. Number and letter drills fill the gaps between fractional sizes, which is why tap drill charts use them. Use the filter to show one series at a time.

Worked check: #29 drill in mm

A #29 drill is 0.1360 in.

Multiply by 25.4: 0.1360 x 25.4 = 3.4544 mm.
Round to 2 places: 3.45 mm.

Result: 3.45 mm, between the 3.4 mm and 3.5 mm metric sizes.

Worked check: 17/64 drill

A 17/64 in fractional drill.

Divide: 17 / 64 = 0.265625 in, shown as 0.2656 in.
Convert: 0.265625 x 25.4 = 6.75 mm.
Nearest letter drill: H (0.266 in).

Result: 17/64 in = 0.2656 in (6.75 mm); an H drill is the closest letter size.

Shop notes

Drill size is nominal. The hole usually drills slightly oversize, more so with a worn or off-center point.
Letter E and 1/4 in are the same size, 0.250 in (6.35 mm). Both rows are listed.
Number drills get smaller as the number goes up: #1 is 0.2280 in, #80 is 0.0135 in.
For a tapped hole, pick the drill from the tap drill chart, then find its size here.

FAQ

What are number and letter drills for?

They fill the gaps between fractional sizes, which is why tap drill charts use them.

What size is a #7 drill?

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

What size is an F drill?

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

Is a letter E drill the same as 1/4 in?

Yes, both are 0.250 in (6.35 mm).

What is the smallest number drill?

#80, 0.0135 in (0.343 mm).

Last updated September 29, 2026

https://webmachinist.net/drillindex.html

How to read the table

Worked check: #29 drill in mm

Worked check: 17/64 drill

Shop notes

FAQ

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