What size is a #7 drill bit?

A #7 drill bit is 0.2010 in (5.105 mm) in diameter — the tap drill for 1/4"-20 UNC at 75% thread engagement.

What are number and letter drill bit sizes?

Two gauge systems that fill the gaps between the fractional sizes. Number drills run from #1 (largest) down to #80 (smallest); letter drills run from A (smallest) to Z (largest) and pick up above the number sizes. Neither is a fraction of an inch — each gauge is a defined decimal diameter, which is why a chart like this one exists.

How many standard drill bit sizes are there?

This chart carries 397 standard sizes: 64 fractional drill sizes, 26 letter drill sizes, 227 metric drill sizes, 60 number drill sizes, plus the smallest number gauges. They span 0.0079 in to 1.0000 in (0.200 mm to 25.400 mm).

Which drill sizes are tap drills?

94 of the sizes in this chart are the shop-default tap drill for at least one standard thread. The tap-drill column links straight to the thread, and each drill page lists every thread it taps with the engagement that drill actually leaves.

Chart · drill sizes

Drill Size Chart — Number, Letter, Fractional and Metric

https://shopmath.org/charts/drill-sizes · data verified August 1, 2026

397 standard drill sizes in one table, from 0.2 mm at 0.0079 in (0.200 mm) to 1" at 1.0000 in (25.400 mm) — number, letter, fractional and metric interleaved by diameter rather than split into four charts. 377 of them have their own page with equivalents and tap sizes. Diameters are nominal.

Sizes: 397
Indexes: 4
Tap drills: 94
Verified: August 1, 2026

Most looked-up row · #7 number drill

0.2010 in

Millimetre: 5.105mm
Taps: 1/4"-20 UNC

Nominal diameter. Full #7 drill bit page →

Drill Size Chart — All Four Indexes Interleaved by Diameter

One table, sorted by diameter, with number, letter, fractional and metric drills in the same column. Filter to one index or sort by series; the full table is present either way.

Series

Sort

397 sizes shown

Drill size chart — number, letter, fractional and metric drills interleaved by diameter
Property	Property	Diameter		Property	Property
Drill	Series	in	mm	Fraction	Tap drill for
0.2 mm	Metric	0.0079	0.200	—	—
0.22 mm	Metric	0.0087	0.220	—	—
0.25 mm	Metric	0.0098	0.250	—	—
0.28 mm	Metric	0.0110	0.280	—	—
0.3 mm	Metric	0.0118	0.300	—	—
0.32 mm	Metric	0.0126	0.320	—	—
#80	Number	0.0135	0.343	—	—
0.35 mm	Metric	0.0138	0.350	—	—
#79	Number	0.0145	0.368	—	—
0.38 mm	Metric	0.0150	0.380	—	—
1/64"	Fractional	0.0156	0.397	1/64	—
0.4 mm	Metric	0.0157	0.400	—	—
#78	Number	0.0160	0.406	—	—
0.42 mm	Metric	0.0165	0.420	—	—
0.45 mm	Metric	0.0177	0.450	—	—
#77	Number	0.0180	0.457	—	—
0.48 mm	Metric	0.0189	0.480	—	—
0.5 mm	Metric	0.0197	0.500	—	—
#76	Number	0.0200	0.508	—	—
0.52 mm	Metric	0.0205	0.520	—	—
#75	Number	0.0210	0.533	—	—
0.55 mm	Metric	0.0217	0.550	—	—
#74	Number	0.0225	0.572	—	—
0.58 mm	Metric	0.0228	0.580	—	—
0.6 mm	Metric	0.0236	0.600	—	—
#73	Number	0.0240	0.610	—	—
0.62 mm	Metric	0.0244	0.620	—	—
#72	Number	0.0250	0.635	—	—
0.65 mm	Metric	0.0256	0.650	—	—
#71	Number	0.0260	0.660	—	—
0.68 mm	Metric	0.0268	0.680	—	—
0.7 mm	Metric	0.0276	0.700	—	—
#70	Number	0.0280	0.711	—	—
0.72 mm	Metric	0.0283	0.720	—	—
#69	Number	0.0292	0.742	—	—
0.75 mm	Metric	0.0295	0.750	—	—
0.78 mm	Metric	0.0307	0.780	—	—
#68	Number	0.0310	0.787	—	—
1/32"	Fractional	0.0313	0.794	1/32	—
0.8 mm	Metric	0.0315	0.800	—	—
#67	Number	0.0320	0.813	—	—
0.82 mm	Metric	0.0323	0.820	—	—
#66	Number	0.0330	0.838	—	—
0.85 mm	Metric	0.0335	0.850	—	—
0.88 mm	Metric	0.0346	0.880	—	—
#65	Number	0.0350	0.889	—	—
0.9 mm	Metric	0.0354	0.900	—	—
#64	Number	0.0360	0.914	—	—
0.92 mm	Metric	0.0362	0.920	—	—
#63	Number	0.0370	0.940	—	—
0.95 mm	Metric	0.0374	0.950	—	—
#62	Number	0.0380	0.965	—	—
0.98 mm	Metric	0.0386	0.980	—	—
#61	Number	0.0390	0.991	—	—
1 mm	Metric	0.0394	1.000	—	—
#60	Number	0.0400	1.016	—	—
#59	Number	0.0410	1.041	—	—
1.05 mm	Metric	0.0413	1.050	—	—
#58	Number	0.0420	1.067	—	—
#57	Number	0.0430	1.092	—	—
1.1 mm	Metric	0.0433	1.100	—	—
1.15 mm	Metric	0.0453	1.150	—	—
#56	Number	0.0465	1.181	—	—
3/64"	Fractional	0.0469	1.191	3/64	#0-80 UNF
1.2 mm	Metric	0.0472	1.200	—	—
1.25 mm	Metric	0.0492	1.250	—	M1.6×0.35
1.3 mm	Metric	0.0512	1.300	—	—
#55	Number	0.0520	1.321	—	—
1.35 mm	Metric	0.0532	1.350	—	—
#54	Number	0.0550	1.397	—	—
1.4 mm	Metric	0.0551	1.400	—	M1.6×0.2
1.45 mm	Metric	0.0571	1.450	—	M1.8×0.35
1.5 mm	Metric	0.0591	1.500	—	—
#53	Number	0.0595	1.511	—	#1-72 UNF #1-64 UNC
1.55 mm	Metric	0.0610	1.550	—	—
1/16"	Fractional	0.0625	1.587	1/16	—
1.6 mm	Metric	0.0630	1.600	—	M1.8×0.2 M2×0.4
#52	Number	0.0635	1.613	—	—
1.65 mm	Metric	0.0650	1.650	—	—
1.7 mm	Metric	0.0669	1.700	—	—
#51	Number	0.0670	1.702	—	—
1.75 mm	Metric	0.0689	1.750	—	M2×0.25
#50	Number	0.0700	1.778	—	#2-64 UNF #2-56 UNC
1.8 mm	Metric	0.0709	1.800	—	—
1.85 mm	Metric	0.0728	1.850	—	—
#49	Number	0.0730	1.854	—	—
1.9 mm	Metric	0.0748	1.900	—	—
#48	Number	0.0760	1.930	—	—
1.95 mm	Metric	0.0768	1.950	—	—
5/64"	Fractional	0.0781	1.984	5/64	—
#47	Number	0.0785	1.994	—	#3-48 UNC
2 mm	Metric	0.0787	2.000	—	—
2.05 mm	Metric	0.0807	2.050	—	M2.5×0.45
#46	Number	0.0810	2.057	—	—
#45	Number	0.0820	2.083	—	#3-56 UNF
2.1 mm	Metric	0.0827	2.100	—	—
2.15 mm	Metric	0.0846	2.150	—	M2.5×0.35
#44	Number	0.0860	2.184	—	—
2.2 mm	Metric	0.0866	2.200	—	—
2.25 mm	Metric	0.0886	2.250	—	—
#43	Number	0.0890	2.261	—	#4-40 UNC
2.3 mm	Metric	0.0906	2.300	—	—
2.35 mm	Metric	0.0925	2.350	—	—
#42	Number	0.0935	2.375	—	#4-48 UNF
3/32"	Fractional	0.0938	2.381	3/32	—
2.4 mm	Metric	0.0945	2.400	—	—
#41	Number	0.0960	2.438	—	—
2.45 mm	Metric	0.0965	2.450	—	—
#40	Number	0.0980	2.489	—	—
2.5 mm	Metric	0.0984	2.500	—	M3×0.5
#39	Number	0.0995	2.527	—	—
2.55 mm	Metric	0.1004	2.550	—	—
#38	Number	0.1015	2.578	—	#5-40 UNC
2.6 mm	Metric	0.1024	2.600	—	—
#37	Number	0.1040	2.642	—	#5-44 UNF
2.65 mm	Metric	0.1043	2.650	—	M3×0.35
2.7 mm	Metric	0.1063	2.700	—	—
#36	Number	0.1065	2.705	—	#6-32 UNC
2.75 mm	Metric	0.1083	2.750	—	—
7/64"	Fractional	0.1094	2.778	7/64	—
#35	Number	0.1100	2.794	—	—
2.8 mm	Metric	0.1102	2.800	—	—
#34	Number	0.1110	2.819	—	—
2.85 mm	Metric	0.1122	2.850	—	—
#33	Number	0.1130	2.870	—	#6-40 UNF
2.9 mm	Metric	0.1142	2.900	—	M3.5×0.6
#32	Number	0.1160	2.946	—	—
2.95 mm	Metric	0.1161	2.950	—	—
3 mm	Metric	0.1181	3.000	—	—
#31	Number	0.1200	3.048	—	—
3.1 mm	Metric	0.1220	3.100	—	—
1/8"	Fractional	0.1250	3.175	1/8	—
3.2 mm	Metric	0.1260	3.200	—	M3.5×0.35
#30	Number	0.1285	3.264	—	—
3.3 mm	Metric	0.1299	3.300	—	M4×0.7
3.4 mm	Metric	0.1339	3.400	—	—
#29	Number	0.1360	3.454	—	#8-36 UNF #8-32 UNC
3.5 mm	Metric	0.1378	3.500	—	M4×0.5
#28	Number	0.1405	3.569	—	—
9/64"	Fractional	0.1406	3.572	9/64	—
3.6 mm	Metric	0.1417	3.600	—	—
#27	Number	0.1440	3.658	—	—
3.7 mm	Metric	0.1457	3.700	—	—
#26	Number	0.1470	3.734	—	—
#25	Number	0.1495	3.797	—	#10-24 UNC
3.8 mm	Metric	0.1496	3.800	—	—
#24	Number	0.1520	3.861	—	—
3.9 mm	Metric	0.1535	3.900	—	—
#23	Number	0.1540	3.912	—	—
5/32"	Fractional	0.1563	3.969	5/32	—
#22	Number	0.1570	3.988	—	—
4 mm	Metric	0.1575	4.000	—	—
#21	Number	0.1590	4.039	—	#10-32 UNF
#20	Number	0.1610	4.089	—	—
4.1 mm	Metric	0.1614	4.100	—	—
4.2 mm	Metric	0.1654	4.200	—	M5×0.8
#19	Number	0.1660	4.216	—	—
4.3 mm	Metric	0.1693	4.300	—	—
#18	Number	0.1695	4.305	—	—
11/64"	Fractional	0.1719	4.366	11/64	—
#17	Number	0.1730	4.394	—	—
4.4 mm	Metric	0.1732	4.400	—	—
#16	Number	0.1770	4.496	—	#12-24 UNC
4.5 mm	Metric	0.1772	4.500	—	M5×0.5
#15	Number	0.1800	4.572	—	—
4.6 mm	Metric	0.1811	4.600	—	—
#14	Number	0.1820	4.623	—	#12-28 UNF
#13	Number	0.1850	4.699	—	#12-32 UNEF
4.7 mm	Metric	0.1850	4.700	—	—
3/16"	Fractional	0.1875	4.763	3/16	—
4.8 mm	Metric	0.1890	4.800	—	—
#12	Number	0.1890	4.801	—	—
#11	Number	0.1910	4.851	—	—
4.9 mm	Metric	0.1929	4.900	—	—
#10	Number	0.1935	4.915	—	—
#9	Number	0.1960	4.978	—	—
5 mm	Metric	0.1968	5.000	—	M6×1
#8	Number	0.1990	5.055	—	—
5.1 mm	Metric	0.2008	5.100	—	—
#7	Number	0.2010	5.105	—	1/4"-20 UNC
13/64"	Fractional	0.2031	5.159	13/64	—
#6	Number	0.2040	5.182	—	—
5.2 mm	Metric	0.2047	5.200	—	—
#5	Number	0.2055	5.220	—	—
5.3 mm	Metric	0.2087	5.300	—	M6×0.75
#4	Number	0.2090	5.309	—	—
5.4 mm	Metric	0.2126	5.400	—	—
#3	Number	0.2130	5.410	—	1/4"-28 UNF
5.5 mm	Metric	0.2165	5.500	—	—
7/32"	Fractional	0.2188	5.556	7/32	1/4"-32 UNEF
5.6 mm	Metric	0.2205	5.600	—	—
#2	Number	0.2210	5.613	—	—
5.7 mm	Metric	0.2244	5.700	—	—
#1	Number	0.2280	5.791	—	—
5.8 mm	Metric	0.2283	5.800	—	—
5.9 mm	Metric	0.2323	5.900	—	—
A	Letter	0.2340	5.944	—	—
15/64"	Fractional	0.2344	5.953	15/64	—
6 mm	Metric	0.2362	6.000	—	M7×1
B	Letter	0.2380	6.045	—	—
6.1 mm	Metric	0.2402	6.100	—	—
C	Letter	0.2420	6.147	—	—
6.2 mm	Metric	0.2441	6.200	—	—
D	Letter	0.2460	6.248	—	—
6.3 mm	Metric	0.2480	6.300	—	M7×0.75
E	Letter	0.2500	6.350	—	—
1/4"	Fractional	0.2500	6.350	1/4	—
6.4 mm	Metric	0.2520	6.400	—	—
6.5 mm	Metric	0.2559	6.500	—	—
F	Letter	0.2570	6.528	—	5/16"-18 UNC
6.6 mm	Metric	0.2598	6.600	—	—
G	Letter	0.2610	6.629	—	—
6.7 mm	Metric	0.2638	6.700	—	—
17/64"	Fractional	0.2656	6.747	17/64	—
H	Letter	0.2660	6.756	—	—
6.8 mm	Metric	0.2677	6.800	—	M8×1.25
6.9 mm	Metric	0.2717	6.900	—	—
I	Letter	0.2720	6.909	—	5/16"-24 UNF
7 mm	Metric	0.2756	7.000	—	M8×1
J	Letter	0.2770	7.036	—	—
7.1 mm	Metric	0.2795	7.100	—	—
K	Letter	0.2810	7.137	—	—
9/32"	Fractional	0.2813	7.144	9/32	5/16"-32 UNEF
7.2 mm	Metric	0.2835	7.200	—	—
7.3 mm	Metric	0.2874	7.300	—	M8×0.75
L	Letter	0.2900	7.366	—	—
7.4 mm	Metric	0.2913	7.400	—	—
M	Letter	0.2950	7.493	—	—
7.5 mm	Metric	0.2953	7.500	—	—
19/64"	Fractional	0.2969	7.541	19/64	—
7.6 mm	Metric	0.2992	7.600	—	—
N	Letter	0.3020	7.671	—	—
7.7 mm	Metric	0.3031	7.700	—	—
7.8 mm	Metric	0.3071	7.800	—	—
7.9 mm	Metric	0.3110	7.900	—	—
5/16"	Fractional	0.3125	7.938	5/16	3/8"-16 UNC
8 mm	Metric	0.3150	8.000	—	—
O	Letter	0.3160	8.026	—	—
8.1 mm	Metric	0.3189	8.100	—	—
8.2 mm	Metric	0.3228	8.200	—	—
P	Letter	0.3230	8.204	—	—
8.3 mm	Metric	0.3268	8.300	—	—
21/64"	Fractional	0.3281	8.334	21/64	—
8.4 mm	Metric	0.3307	8.400	—	—
Q	Letter	0.3320	8.433	—	3/8"-24 UNF
8.5 mm	Metric	0.3346	8.500	—	M10×1.5
8.6 mm	Metric	0.3386	8.600	—	—
R	Letter	0.3390	8.611	—	—
8.7 mm	Metric	0.3425	8.700	—	—
11/32"	Fractional	0.3438	8.731	11/32	3/8"-32 UNEF
8.8 mm	Metric	0.3465	8.800	—	M10×1.25
S	Letter	0.3480	8.839	—	—
8.9 mm	Metric	0.3504	8.900	—	—
9 mm	Metric	0.3543	9.000	—	M10×1
T	Letter	0.3580	9.093	—	—
9.1 mm	Metric	0.3583	9.100	—	—
23/64"	Fractional	0.3594	9.128	23/64	—
9.2 mm	Metric	0.3622	9.200	—	—
9.3 mm	Metric	0.3661	9.300	—	—
U	Letter	0.3680	9.347	—	7/16"-14 UNC
9.4 mm	Metric	0.3701	9.400	—	—
9.5 mm	Metric	0.3740	9.500	—	—
3/8"	Fractional	0.3750	9.525	3/8	—
V	Letter	0.3770	9.576	—	—
9.6 mm	Metric	0.3780	9.600	—	—
9.7 mm	Metric	0.3819	9.700	—	—
9.8 mm	Metric	0.3858	9.800	—	—
W	Letter	0.3860	9.804	—	—
9.9 mm	Metric	0.3898	9.900	—	—
25/64"	Fractional	0.3906	9.922	25/64	7/16"-20 UNF
10 mm	Metric	0.3937	10.000	—	—
X	Letter	0.3970	10.084	—	—
10.1 mm	Metric	0.3976	10.100	—	—
10.2 mm	Metric	0.4016	10.200	—	—
Y	Letter	0.4040	10.262	—	7/16"-28 UNEF
10.3 mm	Metric	0.4055	10.300	—	M12×1.75
13/32"	Fractional	0.4063	10.319	13/32	—
10.4 mm	Metric	0.4094	10.400	—	—
Z	Letter	0.4130	10.490	—	—
10.5 mm	Metric	0.4134	10.500	—	M12×1.5
10.6 mm	Metric	0.4173	10.600	—	—
10.7 mm	Metric	0.4213	10.700	—	—
27/64"	Fractional	0.4219	10.716	27/64	1/2"-13 UNC
10.8 mm	Metric	0.4252	10.800	—	M12×1.25
10.9 mm	Metric	0.4291	10.900	—	—
11 mm	Metric	0.4331	11.000	—	—
11.1 mm	Metric	0.4370	11.100	—	—
7/16"	Fractional	0.4375	11.113	7/16	—
11.2 mm	Metric	0.4409	11.200	—	—
11.3 mm	Metric	0.4449	11.300	—	—
11.4 mm	Metric	0.4488	11.400	—	—
11.5 mm	Metric	0.4528	11.500	—	—
29/64"	Fractional	0.4531	11.509	29/64	1/2"-20 UNF
11.6 mm	Metric	0.4567	11.600	—	—
11.7 mm	Metric	0.4606	11.700	—	—
11.8 mm	Metric	0.4646	11.800	—	—
11.9 mm	Metric	0.4685	11.900	—	—
15/32"	Fractional	0.4688	11.906	15/32	1/2"-28 UNEF
12 mm	Metric	0.4724	12.000	—	—
12.1 mm	Metric	0.4764	12.100	—	M14×2
12.2 mm	Metric	0.4803	12.200	—	—
12.3 mm	Metric	0.4843	12.300	—	—
31/64"	Fractional	0.4844	12.303	31/64	9/16"-12 UNC
12.4 mm	Metric	0.4882	12.400	—	—
12.5 mm	Metric	0.4921	12.500	—	M14×1.5
12.6 mm	Metric	0.4961	12.600	—	—
1/2"	Fractional	0.5000	12.700	1/2	—
12.7 mm	Metric	0.5000	12.700	—	—
12.8 mm	Metric	0.5039	12.800	—	—
12.9 mm	Metric	0.5079	12.900	—	—
13 mm	Metric	0.5118	13.000	—	—
33/64"	Fractional	0.5156	13.097	33/64	9/16"-24 UNEF 9/16"-18 UNF
13.1 mm	Metric	0.5157	13.100	—	—
13.2 mm	Metric	0.5197	13.200	—	—
13.3 mm	Metric	0.5236	13.300	—	—
13.4 mm	Metric	0.5276	13.400	—	—
17/32"	Fractional	0.5313	13.494	17/32	5/8"-11 UNC
13.5 mm	Metric	0.5315	13.500	—	—
13.6 mm	Metric	0.5354	13.600	—	—
13.7 mm	Metric	0.5394	13.700	—	—
13.8 mm	Metric	0.5433	13.800	—	—
35/64"	Fractional	0.5469	13.891	35/64	—
13.9 mm	Metric	0.5472	13.900	—	—
14 mm	Metric	0.5512	14.000	—	M16×2
14.25 mm	Metric	0.5610	14.250	—	—
9/16"	Fractional	0.5625	14.287	9/16	—
14.5 mm	Metric	0.5709	14.500	—	M16×1.5
37/64"	Fractional	0.5781	14.684	37/64	5/8"-24 UNEF 5/8"-18 UNF
14.75 mm	Metric	0.5807	14.750	—	—
15 mm	Metric	0.5906	15.000	—	—
19/32"	Fractional	0.5938	15.081	19/32	—
15.25 mm	Metric	0.6004	15.250	—	—
39/64"	Fractional	0.6094	15.478	39/64	—
15.5 mm	Metric	0.6102	15.500	—	M18×2.5
15.75 mm	Metric	0.6201	15.750	—	—
5/8"	Fractional	0.6250	15.875	5/8	—
16 mm	Metric	0.6299	16.000	—	M18×2
16.25 mm	Metric	0.6398	16.250	—	—
41/64"	Fractional	0.6406	16.272	41/64	11/16"-24 UNEF
16.5 mm	Metric	0.6496	16.500	—	M18×1.5
21/32"	Fractional	0.6563	16.669	21/32	3/4"-10 UNC
16.75 mm	Metric	0.6594	16.750	—	—
17 mm	Metric	0.6693	17.000	—	—
43/64"	Fractional	0.6719	17.066	43/64	—
17.25 mm	Metric	0.6791	17.250	—	—
11/16"	Fractional	0.6875	17.462	11/16	3/4"-16 UNF
17.5 mm	Metric	0.6890	17.500	—	M20×2.5
17.75 mm	Metric	0.6988	17.750	—	—
45/64"	Fractional	0.7031	17.859	45/64	3/4"-20 UNEF
18 mm	Metric	0.7087	18.000	—	M20×2
18.25 mm	Metric	0.7185	18.250	—	—
23/32"	Fractional	0.7188	18.256	23/32	—
18.5 mm	Metric	0.7283	18.500	—	M20×1.5
47/64"	Fractional	0.7344	18.653	47/64	—
18.75 mm	Metric	0.7382	18.750	—	—
19 mm	Metric	0.7480	19.000	—	—
3/4"	Fractional	0.7500	19.050	3/4	—
19.25 mm	Metric	0.7579	19.250	—	—
49/64"	Fractional	0.7656	19.447	49/64	13/16"-20 UNEF 7/8"-9 UNC
19.5 mm	Metric	0.7677	19.500	—	M22×2.5
19.75 mm	Metric	0.7776	19.750	—	—
25/32"	Fractional	0.7813	19.844	25/32	—
20 mm	Metric	0.7874	20.000	—	M22×2
51/64"	Fractional	0.7969	20.241	51/64	—
20.25 mm	Metric	0.7972	20.250	—	—
20.5 mm	Metric	0.8071	20.500	—	M22×1.5
13/16"	Fractional	0.8125	20.637	13/16	7/8"-14 UNF
20.75 mm	Metric	0.8169	20.750	—	—
21 mm	Metric	0.8268	21.000	—	M24×3
53/64"	Fractional	0.8281	21.034	53/64	7/8"-20 UNEF
21.25 mm	Metric	0.8366	21.250	—	—
27/32"	Fractional	0.8438	21.431	27/32	—
21.5 mm	Metric	0.8465	21.500	—	—
21.75 mm	Metric	0.8563	21.750	—	—
55/64"	Fractional	0.8594	21.828	55/64	—
22 mm	Metric	0.8661	22.000	—	M24×2
7/8"	Fractional	0.8750	22.225	7/8	1"-8 UNC
22.25 mm	Metric	0.8760	22.250	—	—
22.5 mm	Metric	0.8858	22.500	—	—
57/64"	Fractional	0.8906	22.622	57/64	15/16"-20 UNEF
22.75 mm	Metric	0.8957	22.750	—	—
23 mm	Metric	0.9055	23.000	—	—
29/32"	Fractional	0.9063	23.019	29/32	—
23.25 mm	Metric	0.9154	23.250	—	—
59/64"	Fractional	0.9219	23.416	59/64	1"-12 UNF
23.5 mm	Metric	0.9252	23.500	—	—
23.75 mm	Metric	0.9350	23.750	—	—
15/16"	Fractional	0.9375	23.813	15/16	—
24 mm	Metric	0.9449	24.000	—	M27×3
61/64"	Fractional	0.9531	24.209	61/64	1"-20 UNEF
24.25 mm	Metric	0.9547	24.250	—	—
24.5 mm	Metric	0.9646	24.500	—	—
31/32"	Fractional	0.9688	24.606	31/32	—
24.75 mm	Metric	0.9744	24.750	—	—
25 mm	Metric	0.9843	25.000	—	M27×2 M30×2 M30×3.5+20
63/64"	Fractional	0.9844	25.003	63/64	1 1/8"-7 UNC
1"	Fractional	1.0000	25.400	1	1 1/16"-18 UNEF 1 1/8"-18 UNEF 1 1/8"-12 UNF+25

Sizes are interleaved by diameter, so a metric drill sits between the inch sizes it falls between. Diameters are nominal — 1 in = 25.4 mm exactly, so the two diameter columns are one value in two units. Sizes without a link are stored for the nearest-drill calculation but do not carry their own page.

The Four Standard Drill Bit Size Indexes

Each index covers a different span, which is why a complete drill set mixes all four.

Coverage of the number, letter, fractional and metric drill indexes
Series	Sizes	Smallest, in	Largest, in	Smallest, mm	Largest, mm
Fractional Drill Sizes	64	0.0156	1.0000	0.397	25.400
Letter Drill Sizes	26	0.2340	0.4130	5.944	10.490
Metric Drill Sizes	227	0.0079	0.9843	0.200	25.000
Number Drill Sizes	60	0.0400	0.2280	1.016	5.791

Ranges cover the sizes that carry their own page. Number gauges #61-#80 are stored for the nearest-drill calculation and appear in the chart above without a link.

Common Questions About Drill Bit Sizes

What size is a #7 drill bit?: A #7 drill bit is 0.2010 in (5.105 mm) in diameter — the tap drill for 1/4"-20 UNC at 75% thread engagement.
What are number and letter drill bit sizes?: Two gauge systems that fill the gaps between the fractional sizes. Number drills run from #1 (largest) down to #80 (smallest); letter drills run from A (smallest) to Z (largest) and pick up above the number sizes. Neither is a fraction of an inch — each gauge is a defined decimal diameter, which is why a chart like this one exists.
How many standard drill bit sizes are there?: This chart carries 397 standard sizes: 64 fractional drill sizes, 26 letter drill sizes, 227 metric drill sizes, 60 number drill sizes, plus the smallest number gauges. They span 0.0079 in to 1.0000 in (0.200 mm to 25.400 mm).
Which drill sizes are tap drills?: 94 of the sizes in this chart are the shop-default tap drill for at least one standard thread. The tap-drill column links straight to the thread, and each drill page lists every thread it taps with the engagement that drill actually leaves.

Sources and Method for This Drill Size Chart

Standard drill index — number, letter, fractional, metriccomputed+compiled

bd_warehouse drill_sizes.csv (Apache-2.0) + Wikipedia Drill bit sizes (CC BY-SA 4.0); fractional and metric computed from ANSI B94.11M / BS 328 increment patterns

Verified against drills: 31 checks passed across 1 harness(es)

Part computed from the standard's formulas, part compiled from agreeing public sources.

Formula

Fractional drill diameters

Ø  =  n ÷ 64 in,  n = 1 … 64

Fractional drills are exact fractions, computed rather than transcribed; the decimal column is the fraction evaluated.

Inch ↔ millimetre

1 in  ≡  25.4 mm

Exact by definition (international yard and pound agreement, 1959), so the two diameter columns are one value in two units.

Assumptions

Diameters are nominal. Manufacturing tolerance, wear and run-out all cut oversize, which leaves less thread in a tapped hole than the table says.
The tap-drill column shows the shop-default engagement only; the full 50–85% matrix is on the tap drill chart and on each thread page.
Dataset scope: Number sizes #61-#80 are stored but tagged demandTier 'extended' — query-space-map.md Appendix A found the tail thinning in the 60s. Sizes below #80 and metric sizes above 25.0 mm excluded.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This Drill Size Chart

Citation

ShopMath. "Drill Size Chart — Number, Letter, Fractional and Metric." ShopMath, verified August 1, 2026, https://shopmath.org/charts/drill-sizes

BibTeX

@misc{shopmath-charts-drill-sizes,
  title        = {Drill Size Chart — Number, Letter, Fractional and Metric},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/charts/drill-sizes}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/charts/drill-sizes

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