Drill Size Chart

Name: Drill Size Chart
Creator: Manufacturing Processes

Every number, letter, fractional and common metric drill with its decimal inch and millimeter diameter, per ANSI/ASME B94.11M.

Tables: 4
Rows: 274
Units: in, mm
References: 2
Revised: 2026-08-11

Number drills (#1 – #80)

80 rows

Drill	Diameterin	Diametermm
#80	0.0135	0.343
#79	0.0145	0.368
#78	0.016	0.406
#77	0.018	0.457
#76	0.02	0.508
#75	0.021	0.533
#74	0.0225	0.571
#73	0.024	0.61
#72	0.025	0.635
#71	0.026	0.66
#70	0.028	0.711
#69	0.0292	0.742
#68	0.031	0.787
#67	0.032	0.813
#66	0.033	0.838
#65	0.035	0.889
#64	0.036	0.914
#63	0.037	0.94
#62	0.038	0.965
#61	0.039	0.991
#60	0.04	1.016
#59	0.041	1.041
#58	0.042	1.067
#57	0.043	1.092
#56	0.0465	1.181
#55	0.052	1.321
#54	0.055	1.397
#53	0.0595	1.511
#52	0.0635	1.613
#51	0.067	1.702
#50	0.07	1.778
#49	0.073	1.854
#48	0.076	1.93
#47	0.0785	1.994
#46	0.081	2.057
#45	0.082	2.083
#44	0.086	2.184
#43	0.089	2.261
#42	0.0935	2.375
#41	0.096	2.438
#40	0.098	2.489
#39	0.0995	2.527
#38	0.1015	2.578
#37	0.104	2.642
#36	0.1065	2.705
#35	0.11	2.794
#34	0.111	2.819
#33	0.113	2.87
#32	0.116	2.946
#31	0.12	3.048
#30	0.1285	3.264
#29	0.136	3.454
#28	0.1405	3.569
#27	0.144	3.658
#26	0.147	3.734
#25	0.1495	3.797
#24	0.152	3.861
#23	0.154	3.912
#22	0.157	3.988
#21	0.159	4.039
#20	0.161	4.089
#19	0.166	4.216
#18	0.1695	4.305
#17	0.173	4.394
#16	0.177	4.496
#15	0.18	4.572
#14	0.182	4.623
#13	0.185	4.699
#12	0.189	4.801
#11	0.191	4.851
#10	0.1935	4.915
#9	0.196	4.978
#8	0.199	5.055
#7	0.201	5.105
#6	0.204	5.182
#5	0.2055	5.22
#4	0.209	5.309
#3	0.213	5.41
#2	0.221	5.613
#1	0.228	5.791
No rows match that filter.

80 rows × 3 columnsUnits: in, mm

Basis and references

Read before use

Four drill size systems coexist on a US shop floor and none of them supersedes the others: number drills (#1 to #80, larger number = smaller drill), letter drills (A to Z, larger letter = larger drill), fractional drills in 64ths of an inch, and metric drills. A single tap chart will routinely send you to all four.

Diameters below are the nominal values from ANSI/ASME B94.11M. The millimeter columns on the inch systems, and the inch columns on the metric system, are computed at exactly 25.4 mm/in rather than transcribed. Fractional decimals are computed from the fraction itself, so they are exact — a 64th of an inch is exactly representable in decimal.

Note that letter E and 1/4 in are the same nominal diameter (0.2500 in). That duplication is in the standard, not an error in the table.

References

Every value on this page was set against at least two of these sources and recomputed rather than transcribed. Where they disagree, the disagreement is recorded in the notes below.

Letter drills (A – Z)

26 rows

Drill	Diameterin	Diametermm
A	0.234	5.944
B	0.238	6.045
C	0.242	6.147
D	0.246	6.248
E	0.25	6.35
F	0.257	6.528
G	0.261	6.629
H	0.266	6.756
I	0.272	6.909
J	0.277	7.036
K	0.281	7.137
L	0.29	7.366
M	0.295	7.493
N	0.302	7.671
O	0.316	8.026
P	0.323	8.204
Q	0.332	8.433
R	0.339	8.611
S	0.348	8.839
T	0.358	9.093
U	0.368	9.347
V	0.377	9.576
W	0.386	9.804
X	0.397	10.084
Y	0.404	10.262
Z	0.413	10.49
No rows match that filter.

26 rows × 3 columnsUnits: in, mm

Fractional drills (1/64 in – 1 in, by 64ths)

64 rows

Fraction	Diameter, exactin	Diametermm
1/64	0.015625	0.3969
1/32	0.03125	0.7937
3/64	0.046875	1.1906
1/16	0.0625	1.5875
5/64	0.078125	1.9844
3/32	0.09375	2.3812
7/64	0.109375	2.7781
1/8	0.125	3.175
9/64	0.140625	3.5719
5/32	0.15625	3.9688
11/64	0.171875	4.3656
3/16	0.1875	4.7625
13/64	0.203125	5.1594
7/32	0.21875	5.5562
15/64	0.234375	5.9531
1/4	0.25	6.35
17/64	0.265625	6.7469
9/32	0.28125	7.1437
19/64	0.296875	7.5406
5/16	0.3125	7.9375
21/64	0.328125	8.3344
11/32	0.34375	8.7312
23/64	0.359375	9.1281
3/8	0.375	9.525
25/64	0.390625	9.9219
13/32	0.40625	10.3187
27/64	0.421875	10.7156
7/16	0.4375	11.1125
29/64	0.453125	11.5094
15/32	0.46875	11.9062
31/64	0.484375	12.3031
1/2	0.5	12.7
33/64	0.515625	13.0969
17/32	0.53125	13.4937
35/64	0.546875	13.8906
9/16	0.5625	14.2875
37/64	0.578125	14.6844
19/32	0.59375	15.0812
39/64	0.609375	15.4781
5/8	0.625	15.875
41/64	0.640625	16.2719
21/32	0.65625	16.6687
43/64	0.671875	17.0656
11/16	0.6875	17.4625
45/64	0.703125	17.8594
23/32	0.71875	18.2562
47/64	0.734375	18.6531
3/4	0.75	19.05
49/64	0.765625	19.4469
25/32	0.78125	19.8438
51/64	0.796875	20.2406
13/16	0.8125	20.6375
53/64	0.828125	21.0344
27/32	0.84375	21.4312
55/64	0.859375	21.8281
7/8	0.875	22.225
57/64	0.890625	22.6219
29/32	0.90625	23.0187
59/64	0.921875	23.4156
15/16	0.9375	23.8125
61/64	0.953125	24.2094
31/32	0.96875	24.6062
63/64	0.984375	25.0031
1	1	25.4
No rows match that filter.

64 rows × 3 columnsUnits: in, mm

Common metric drills (0.5 – 13.0 mm)

104 rows

Drill	Diametermm	Diameterin
0.5 mm	0.5	0.0197
0.6 mm	0.6	0.0236
0.7 mm	0.7	0.0276
0.8 mm	0.8	0.0315
0.9 mm	0.9	0.0354
1 mm	1	0.0394
1.1 mm	1.1	0.0433
1.2 mm	1.2	0.0472
1.25 mm	1.25	0.0492
1.3 mm	1.3	0.0512
1.4 mm	1.4	0.0551
1.5 mm	1.5	0.0591
1.6 mm	1.6	0.063
1.7 mm	1.7	0.0669
1.75 mm	1.75	0.0689
1.8 mm	1.8	0.0709
1.9 mm	1.9	0.0748
2 mm	2	0.0787
2.1 mm	2.1	0.0827
2.2 mm	2.2	0.0866
2.25 mm	2.25	0.0886
2.3 mm	2.3	0.0906
2.4 mm	2.4	0.0945
2.5 mm	2.5	0.0984
2.6 mm	2.6	0.1024
2.7 mm	2.7	0.1063
2.75 mm	2.75	0.1083
2.8 mm	2.8	0.1102
2.9 mm	2.9	0.1142
3 mm	3	0.1181
3.1 mm	3.1	0.122
3.2 mm	3.2	0.126
3.25 mm	3.25	0.128
3.3 mm	3.3	0.1299
3.4 mm	3.4	0.1339
3.5 mm	3.5	0.1378
3.6 mm	3.6	0.1417
3.7 mm	3.7	0.1457
3.75 mm	3.75	0.1476
3.8 mm	3.8	0.1496
3.9 mm	3.9	0.1535
4 mm	4	0.1575
4.1 mm	4.1	0.1614
4.2 mm	4.2	0.1654
4.25 mm	4.25	0.1673
4.3 mm	4.3	0.1693
4.4 mm	4.4	0.1732
4.5 mm	4.5	0.1772
4.6 mm	4.6	0.1811
4.7 mm	4.7	0.185
4.75 mm	4.75	0.187
4.8 mm	4.8	0.189
4.9 mm	4.9	0.1929
5 mm	5	0.1969
5.1 mm	5.1	0.2008
5.2 mm	5.2	0.2047
5.25 mm	5.25	0.2067
5.3 mm	5.3	0.2087
5.4 mm	5.4	0.2126
5.5 mm	5.5	0.2165
5.6 mm	5.6	0.2205
5.7 mm	5.7	0.2244
5.75 mm	5.75	0.2264
5.8 mm	5.8	0.2283
5.9 mm	5.9	0.2323
6 mm	6	0.2362
6.1 mm	6.1	0.2402
6.2 mm	6.2	0.2441
6.25 mm	6.25	0.2461
6.3 mm	6.3	0.248
6.4 mm	6.4	0.252
6.5 mm	6.5	0.2559
6.6 mm	6.6	0.2598
6.7 mm	6.7	0.2638
6.75 mm	6.75	0.2657
6.8 mm	6.8	0.2677
6.9 mm	6.9	0.2717
7 mm	7	0.2756
7.1 mm	7.1	0.2795
7.2 mm	7.2	0.2835
7.25 mm	7.25	0.2854
7.3 mm	7.3	0.2874
7.4 mm	7.4	0.2913
7.5 mm	7.5	0.2953
7.6 mm	7.6	0.2992
7.7 mm	7.7	0.3031
7.75 mm	7.75	0.3051
7.8 mm	7.8	0.3071
7.9 mm	7.9	0.311
8 mm	8	0.315
8.25 mm	8.25	0.3248
8.5 mm	8.5	0.3346
8.75 mm	8.75	0.3445
9 mm	9	0.3543
9.25 mm	9.25	0.3642
9.5 mm	9.5	0.374
9.75 mm	9.75	0.3839
10 mm	10	0.3937
10.5 mm	10.5	0.4134
11 mm	11	0.4331
11.5 mm	11.5	0.4528
12 mm	12	0.4724
12.5 mm	12.5	0.4921
13 mm	13	0.5118
No rows match that filter.

104 rows × 3 columnsUnits: mm, in

Revision and twin

2026-08-11

Last reviewed 2026-08-11. This page carries 274 rows across 4 tables, all of them in the HTML — nothing is paginated, gated or fetched.

Plain-Markdown twin: /charts/drill-size-chart.md

Notes to the tables

4 notes

Where this data disagrees with itself, with other published charts, or with what the number looks like it means.

Letter K is 0.2810 in, not 0.2811 in. Engineers Edge publishes 0.2811; Wikipedia and Machinery's Handbook give 0.2810, which is the value in ASME B94.11M and in every drill manufacturer's catalog. The Engineers Edge figure looks like a transcription artefact from the adjacent 9/32 = 0.28125 row. The 0.0001 in difference sits below drill manufacturing tolerance, so it will never matter at the machine — but this chart publishes four-place decimals, so it matters here.
Several published fractional decimals are truncated rather than rounded. Engineers Edge shows 11/32 as .3437 (correctly .3438), 15/32 as .4687 (.4688), 19/32 as .5937 (.5938), 23/32 as .7187 (.7188), 27/32 as .8437 (.8438) and 31/32 as .9687 (.9688). Because this chart computes fractional decimals from the fraction, none of that propagates.
Shop-floor names are not a second size. Machinists call fractional drills by an abbreviated decimal — 27/64 is "a four-twenty-one drill", 1/16 is "a sixty-two". That shorthand is inconsistent (it rounds in some places and follows tradition in others), so it is deliberately not tabulated here. The exact decimal is the one to work from.
All 80 number drills and all 26 letter drills were cross-checked cell by cell against two independent sources.

Questions

6 questions

What size is a #7 drill?

A #7 drill is 0.2010 in (5.105 mm). It is the standard tap drill for a 1/4-20 UNC thread at roughly 75% engagement.

Do number drills get bigger or smaller as the number goes up?

Smaller. #1 is the largest at 0.2280 in and #80 is the smallest at 0.0135 in. Letter drills run the other way: A is the smallest at 0.2340 in and Z the largest at 0.4130 in.

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

1/4 in is exactly 6.350 mm. The nearest stocked metric drills are 6.3 mm (0.2480 in) and 6.4 mm (0.2520 in), so neither is an exact substitute.

Why do letter E and 1/4 in have the same diameter?

Because they genuinely do: both are 0.2500 in. The letter and fractional series overlap in places and ASME B94.11M lists both designations. It is a duplicate name, not a duplicate size.

What is the largest number drill and the smallest letter drill?

The largest number drill is #1 at 0.2280 in; the smallest letter drill is A at 0.2340 in. The series are contiguous, so the letter drills pick up where the number drills leave off.

How precise are these decimals?

Number and letter drill diameters are the nominal values from ANSI/ASME B94.11M, cross-checked cell by cell against two sources. Fractional decimals are computed exactly from the fraction, and the metric-to-inch conversions use exactly 25.4 mm/in.

How to cite this page

Manufacturing Processes. “Drill Size Chart.” manufacturingprocesses.org, last reviewed 2026-08-11. https://manufacturingprocesses.org/charts/drill-size-chart

If you reproduce a table, cite the standard it derives from as well — the references are the primary sources, this page is a cross-checked transcription of them.