Drill Bit Diameter Chart: Fractional, Number & Metric

Use this drill bit diameter chart to translate fractional, number, letter and metric drill designations into nominal diameters. It covers fractional drills from 1/64 through 1 inch, number drills #80 through #1, letter drills A through Z and common metric sizes.

The listed diameter describes the drill, not a guaranteed finished hole. Choose the required hole first, select the corresponding drill and measure the result where fit matters.

Enter the required diameter to find exact or adjacent drill sizes.

How Drill Size Designations Compare

• Number drills run backward: #80 is the smallest in this chart; #1 is the largest.
• Letter drills run upward: A is smaller than B, and Z is the largest letter drill.
• Fractional values are exact: decimal inches are shown to six places and millimeters to three.
• Number and letter sizes are nominal decimal-inch diameters: their millimeter equivalents are rounded to three places.
• Metric drills do not need an equivalent inch drill: the decimal-inch value is provided for comparison.

The inch-to-metric calculations use the exact relationship 1 inch = 25.4 mm, as documented by NIST. Number and letter values are documented in the ICS Cutting Tools conversion chart and Fastenal’s decimal-equivalents chart. Fastenal’s 2024 jobber-drill product standard also lists #60 through #1, A through Z, fractional drills through 1/2 inch and selected metric sizes.

Fractional Drill Diameters From 1/64 To 1 Inch

Size	Decimal in.	mm
1/64	0.015625	0.397
1/32	0.031250	0.794
3/64	0.046875	1.191
1/16	0.062500	1.588
5/64	0.078125	1.984
3/32	0.093750	2.381
7/64	0.109375	2.778
1/8	0.125000	3.175
9/64	0.140625	3.572
5/32	0.156250	3.969
11/64	0.171875	4.366
3/16	0.187500	4.763
13/64	0.203125	5.159
7/32	0.218750	5.556
15/64	0.234375	5.953
1/4	0.250000	6.350
17/64	0.265625	6.747
9/32	0.281250	7.144
19/64	0.296875	7.541
5/16	0.312500	7.938
21/64	0.328125	8.334
11/32	0.343750	8.731
23/64	0.359375	9.128
3/8	0.375000	9.525
25/64	0.390625	9.922
13/32	0.406250	10.319
27/64	0.421875	10.716
7/16	0.437500	11.113
29/64	0.453125	11.509
15/32	0.468750	11.906
31/64	0.484375	12.303
1/2	0.500000	12.700
33/64	0.515625	13.097
17/32	0.531250	13.494
35/64	0.546875	13.891
9/16	0.562500	14.288
37/64	0.578125	14.684
19/32	0.593750	15.081
39/64	0.609375	15.478
5/8	0.625000	15.875
41/64	0.640625	16.272
21/32	0.656250	16.669
43/64	0.671875	17.066
11/16	0.687500	17.463
45/64	0.703125	17.859
23/32	0.718750	18.256
47/64	0.734375	18.653
3/4	0.750000	19.050
49/64	0.765625	19.447
25/32	0.781250	19.844
51/64	0.796875	20.241
13/16	0.812500	20.638
53/64	0.828125	21.034
27/32	0.843750	21.431
55/64	0.859375	21.828
7/8	0.875000	22.225
57/64	0.890625	22.622
29/32	0.906250	23.019
59/64	0.921875	23.416
15/16	0.937500	23.813
61/64	0.953125	24.209
31/32	0.968750	24.606
63/64	0.984375	25.003
1	1.000000	25.400

Number Drill Diameters From #80 To #1

Size	Decimal in.	mm
#80	0.0135	0.343
#79	0.0145	0.368
#78	0.0160	0.406
#77	0.0180	0.457
#76	0.0200	0.508
#75	0.0210	0.533
#74	0.0225	0.572
#73	0.0240	0.610
#72	0.0250	0.635
#71	0.0260	0.660
#70	0.0280	0.711
#69	0.0292	0.742
#68	0.0310	0.787
#67	0.0320	0.813
#66	0.0330	0.838
#65	0.0350	0.889
#64	0.0360	0.914
#63	0.0370	0.940
#62	0.0380	0.965
#61	0.0390	0.991
#60	0.0400	1.016
#59	0.0410	1.041
#58	0.0420	1.067
#57	0.0430	1.092
#56	0.0465	1.181
#55	0.0520	1.321
#54	0.0550	1.397
#53	0.0595	1.511
#52	0.0635	1.613
#51	0.0670	1.702
#50	0.0700	1.778
#49	0.0730	1.854
#48	0.0760	1.930
#47	0.0785	1.994
#46	0.0810	2.057
#45	0.0820	2.083
#44	0.0860	2.184
#43	0.0890	2.261
#42	0.0935	2.375
#41	0.0960	2.438
#40	0.0980	2.489
#39	0.0995	2.527
#38	0.1015	2.578
#37	0.1040	2.642
#36	0.1065	2.705
#35	0.1100	2.794
#34	0.1110	2.819
#33	0.1130	2.870
#32	0.1160	2.946
#31	0.1200	3.048
#30	0.1285	3.264
#29	0.1360	3.454
#28	0.1405	3.569
#27	0.1440	3.658
#26	0.1470	3.734
#25	0.1495	3.797
#24	0.1520	3.861
#23	0.1540	3.912
#22	0.1570	3.988
#21	0.1590	4.039
#20	0.1610	4.089
#19	0.1660	4.216
#18	0.1695	4.305
#17	0.1730	4.394
#16	0.1770	4.496
#15	0.1800	4.572
#14	0.1820	4.623
#13	0.1850	4.699
#12	0.1890	4.801
#11	0.1910	4.851
#10	0.1935	4.915
#9	0.1960	4.978
#8	0.1990	5.055
#7	0.2010	5.105
#6	0.2040	5.182
#5	0.2055	5.220
#4	0.2090	5.309
#3	0.2130	5.410
#2	0.2210	5.613
#1	0.2280	5.791

Letter Drill Diameters From A To Z

Size	Decimal in.	mm
A	0.2340	5.944
B	0.2380	6.045
C	0.2420	6.147
D	0.2460	6.248
E	0.2500	6.350
F	0.2570	6.528
G	0.2610	6.629
H	0.2660	6.756
I	0.2720	6.909
J	0.2770	7.036
K	0.2810	7.137
L	0.2900	7.366
M	0.2950	7.493
N	0.3020	7.671
O	0.3160	8.026
P	0.3230	8.204
Q	0.3320	8.433
R	0.3390	8.611
S	0.3480	8.839
T	0.3580	9.093
U	0.3680	9.347
V	0.3770	9.576
W	0.3860	9.804
X	0.3970	10.084
Y	0.4040	10.262
Z	0.4130	10.490

Common Metric Drill Diameters In 0.5 mm Steps

Metric drills are sold in more increments than this compact table can show. These 0.5 mm steps are reference points, not a claim that the nearest fractional, number or letter drill is interchangeable.

Metric size	Decimal in.
0.5 mm	0.0197
1.0 mm	0.0394
1.5 mm	0.0591
2.0 mm	0.0787
2.5 mm	0.0984
3.0 mm	0.1181
3.5 mm	0.1378
4.0 mm	0.1575
4.5 mm	0.1772
5.0 mm	0.1969
5.5 mm	0.2165
6.0 mm	0.2362
6.5 mm	0.2559
7.0 mm	0.2756
7.5 mm	0.2953
8.0 mm	0.3150
8.5 mm	0.3346
9.0 mm	0.3543
9.5 mm	0.3740
10.0 mm	0.3937
10.5 mm	0.4134
11.0 mm	0.4331
11.5 mm	0.4528
12.0 mm	0.4724
12.5 mm	0.4921
13.0 mm	0.5118

Choose The Hole Requirement Before The Nearest Drill

Do not automatically select the drill with the smallest numerical difference. Decide what the hole must do.

• Tapped hole: Use the tap maker’s drill recommendation for the complete thread marking and tap type. A standard cutting tap, forming tap, STI tap and pipe tap can require different holes. Compare the choices for a 1/4-inch tap and a 1/2-13 cutting tap.
• Bolt clearance hole: Use the specified close, normal or loose fit rather than matching the bolt’s nominal diameter. The difference is illustrated by the M6 clearance-hole sizes.
• Dowel, bearing or precision fit: Drilling alone may only be the roughing operation. Leave the required stock and finish by boring or reaming to the drawing requirement.
• Unknown replacement part: Record the feature and measurement location before choosing a nominal size. A measured worn hole is not automatically the original drawing diameter.

If substituting because the specified drill is unavailable, calculate the difference first. Letter F is 0.2570 inch while 1/4 inch is 0.2500 inch. The F drill is 0.0070 inch larger, not another name for a 1/4-inch drill.

Nominal Drill Diameter Does Not Guarantee Hole Diameter

A chart value is nominal. Fastenal’s 2024 jobber-drill standard cited above permits minus diameter tolerances that vary with drill range. Its requirements include 0 to −0.0007 inch for #30 through #1 drills and 0 to −0.0010 inch for F through Z drills. Those tolerances apply to that drill line, not universally to every drill.

The hole introduces another set of variables. OSG’s drilling technical guide identifies tool runout, cutting conditions, drill geometry, workpiece shape and clamping among the factors affecting hole accuracy. It specifically notes that runout and vibration can enlarge a drilled hole.

For a fit-sensitive job:

1. Confirm the size designation and inspect the cutting edges.
2. Measure the drill across its margins with a suitable micrometer if its identity is uncertain.
3. Clamp the work rigidly and minimize chuck or holder runout.
4. Drill a test hole in the same material and thickness when scrap is available.
5. Deburr without rolling a large chamfer into the measuring surface.
6. Measure the finished hole with an appropriate pin, plug gauge or bore-measuring tool.

That final measurement is the finished-part result. The chart remains the nominal tool reference.