Engineering · Reference

Drill size chart — every standard size, sorted.

Number, letter, fractional, and metric drills cross-referenced by decimal-inch equivalent. Search over 130 standard sizes, simulate sizing on a high-fidelity digital caliper, test gauge hole template alignments, and instantly calculate thread clearance matches.

Number drills

#80 → #1

Letter drills

A → Z

Fractional

1/64 → 1″

Metric

0.5 → 25 mm

Search & Filter

Drill Size Finder

Measurement Laboratory

Interactive Digital Caliper Gauge

Unit:

Physical Scale Ratio Selected size matches #80 micro drill

Index Scale Profile

Circular Drill Index Plate

Scale shows how the selected drill bit inserts relative to a standard fractional index template plate.

Fastener Integration

Clearance & Tap Suitability

Fits are calculated against ASME B1.1 (UNC/UNF) & ISO 262 thread standards.

Data Reference

Complete Drill Size Master Database

Drill	Type	Decimal (in)	Metric (mm)
#80	number	0.0135	0.34
1/64	fractional	0.0156	0.40
0.5 mm	metric	0.0197	0.50
#75	number	0.0210	0.53
#70	number	0.0280	0.71
1/32	fractional	0.0313	0.80
#65	number	0.0350	0.89
1.0 mm	metric	0.0394	1.00
#60	number	0.0400	1.02
3/64	fractional	0.0469	1.19
#55	number	0.0520	1.32
1.5 mm	metric	0.0591	1.50
1/16	fractional	0.0625	1.59
#52	number	0.0635	1.61
#50	number	0.0700	1.78
#48	number	0.0760	1.93
5/64	fractional	0.0781	1.98
2.0 mm	metric	0.0787	2.00
#46	number	0.0810	2.06
#44	number	0.0860	2.18
#42	number	0.0935	2.37
3/32	fractional	0.0938	2.38
#40	number	0.0980	2.49
2.5 mm	metric	0.0984	2.50
#38	number	0.1015	2.58
#36	number	0.1065	2.71
7/64	fractional	0.1094	2.78
#34	number	0.1110	2.82
#32	number	0.1160	2.95
3.0 mm	metric	0.1181	3.00
1/8	fractional	0.1250	3.18
#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	0.1563	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
#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
5.0 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
6.0 mm	metric	0.2362	6.00
B	letter	0.2380	6.05
C	letter	0.2420	6.15
D	letter	0.2460	6.25
E	letter	0.2500	6.35
1/4	fractional	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
7.0 mm	metric	0.2756	7.00
J	letter	0.2770	7.04
K	letter	0.2810	7.14
9/32	fractional	0.2813	7.15
L	letter	0.2900	7.37
M	letter	0.2950	7.49
19/64	fractional	0.2969	7.54
N	letter	0.3020	7.67
5/16	fractional	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	fractional	0.3281	8.33
Q	letter	0.3320	8.43
R	letter	0.3390	8.61
11/32	fractional	0.3438	8.73
S	letter	0.3480	8.84
9.0 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
3/8	fractional	0.3750	9.53
V	letter	0.3770	9.58
W	letter	0.3860	9.80
25/64	fractional	0.3906	9.92
10.0 mm	metric	0.3937	10.00
X	letter	0.3970	10.08
Y	letter	0.4040	10.26
13/32	fractional	0.4063	10.32
Z	letter	0.4130	10.49
27/64	fractional	0.4219	10.72
11.0 mm	metric	0.4331	11.00
7/16	fractional	0.4375	11.11
29/64	fractional	0.4531	11.51
15/32	fractional	0.4688	11.91
12.0 mm	metric	0.4724	12.00
31/64	fractional	0.4844	12.30
1/2	fractional	0.5000	12.70
14.0 mm	metric	0.5512	14.00
9/16	fractional	0.5625	14.29
5/8	fractional	0.6250	15.88
16.0 mm	metric	0.6299	16.00
11/16	fractional	0.6875	17.46
18.0 mm	metric	0.7087	18.00
3/4	fractional	0.7500	19.05
20.0 mm	metric	0.7874	20.00
13/16	fractional	0.8125	20.64
7/8	fractional	0.8750	22.23
15/16	fractional	0.9375	23.81
25.0 mm	metric	0.9843	25.00
1"	fractional	1.0000	25.40

Technical Reference

Drill Classification Standards

Number Drills (#80 to #1)

Inch-system micro holes. Standard in tap-drill charts for #0 through 1/4″ fastener sizes. For example, a #7 (0.2010″) is the absolute industrial standard tap drill size for standard 1/4-20 UNC internal threads.
Letter Drills (A to Z)

Inch-system mid-sized drills spanning 0.234″ to 0.413″. Letter drills bridge the gaps between standard number drills and fractional 1/2″ sizes. The iconic E drill measures exactly 0.2500″, while F and O are typical tap/clearance sizes for 5/16″ standard screws.
Fractional Drills (1/64 to 1″)

The traditional machine shop standard for general clearance holes, bolts, custom axles, and mounting pins. Standardly available in 1/64″ increments through 1″ (ASME B94.11M continues 1/64″ steps to ~1-3/4″, then coarser steps); the table on this page lists a common subset — 1/64″ steps to 1/2″, then 1/16″ steps to 1″.
Metric Drills (0.5 to 25 mm)

Standard metric dimensions widely preferred in international design, automotive brackets, and electronics housing. An excellent baseline: M6 standard threads require a 5.0 mm tap drill, while M8 requires a 6.8 mm tap drill.

Keep exploring

Related tools & references

Tap drill calculator→

Get the correct drill for any thread and target percent of engagement.

Thread specs chart→

UNC, UNF, and metric pitches, majors, and tap drills.

Clearance hole chart→

Close, normal, and loose clearance holes for bolt pass-through.

Countersink & counterbore chart→

Head clearance dimensions for flat-head and socket-head screws.

Thread engagement calculator→

Minimum thread depth to develop full fastener strength.

Technically reviewed by the True Precision Machining engineering team · Last reviewed June 2026

Standards referenced: ASME B1.1, ISO 262, ASME B94.11M

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