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Drill Size Converter

Four sizing systems are alive in the same workshop: metric, fractional inch, number gauge and letter gauge. Type a size in any one of them and get the other three — plus the bit you can actually order. 299 sizes, no sign-up.

Instant converter

Look up any drill size

Type a size in any system — #11, 6.8, 3/16", F, or a thread like M8 — and get the other three plus the bit to actually order.

What it accepts

The box understands every notation these sizes get written in, because drawings, tap charts and catalogues all use different ones:

Metric: 6.8 · 6.8 mm · 12.5
Fractional inch: 3/16 · 3/16" · 0.25 in
Number gauge: #11 · no.11 · number 11
Letter gauge: F · letter Q
By thread: M8 · M2.5 — returns the tap drill
By wall plug: red plug · yellow · brown

The one rule that matters when substituting

The “buy this bit” column rounds to a real stock size, which means it is almost never mathematically exact. Whether that matters depends entirely on which hole you are drilling:

Tap drills — round up, never down. An undersized tap drill leaves too much material and the tap snaps in the hole. Rounding up 0.05–0.1 mm costs a few percent of thread engagement and nothing else.
Clearance holes — do not go far over. The bolt has to pass, but a sloppy hole loses bearing area under the head. Up to about +0.2 mm is fine.
Reamed or dowel holes — do not substitute. If the drawing tolerances the hole, the gauge size is the size.
Anything hand-held — stop worrying. A hand drill wanders more than the 0.03 mm between #58 and #59.

Working from a thread rather than a diameter? The tap drill calculator takes engagement percentage into account, which a size chart cannot.

Complete drill size table

Every size in all four systems, sorted by diameter — 299 entries. Filter it instead of scrolling: the box below matches names, millimetres, decimal inches and uses.

299 sizes shown

Size	mm	Inch	Fraction	Commonly used for
#80	0.34	0.0135	≈ 1/64"
#79	0.37	0.0145	≈ 1/64"
1/64"	0.40	0.0156	1/64"
#78	0.41	0.0160	1/64"
#77	0.46	0.0180	≈ 1/64"
0.5 mm	0.50	0.0197	≈ 1/64"
#76	0.51	0.0200	≈ 1/64"
#75	0.53	0.0210	≈ 1/64"
#74	0.57	0.0225	≈ 1/64"
0.6 mm	0.60	0.0236	≈ 1/32"
#73	0.61	0.0240	≈ 1/32"
#72	0.64	0.0250	≈ 1/32"
#71	0.66	0.0260	≈ 1/32"
0.7 mm	0.70	0.0276	≈ 1/32"
#70	0.71	0.0280	≈ 1/32"
#69	0.74	0.0292	≈ 1/32"
#68	0.79	0.0310	1/32"
1/32"	0.79	0.0313	1/32"
0.8 mm	0.80	0.0315	1/32"
#67	0.81	0.0320	≈ 1/32"
#66	0.84	0.0330	≈ 1/32"
#65	0.89	0.0350	≈ 1/32"
0.9 mm	0.90	0.0354	≈ 1/32"
#64	0.91	0.0360	≈ 1/32"
#63	0.94	0.0370	≈ 1/32"
#62	0.97	0.0380	≈ 1/32"
#61	0.99	0.0390	≈ 1/32"
1 mm	1.00	0.0394	≈ 3/64"
#60	1.02	0.0400	≈ 3/64"
#59	1.04	0.0410	≈ 3/64"
#58	1.07	0.0420	≈ 3/64"
#57	1.09	0.0430	≈ 3/64"
1.1 mm	1.10	0.0433	≈ 3/64"
#56	1.18	0.0465	3/64"
3/64"	1.19	0.0469	3/64"
1.2 mm	1.20	0.0472	3/64"
1.3 mm	1.30	0.0512	≈ 3/64"
#55	1.32	0.0520	≈ 3/64"
#54	1.40	0.0550	≈ 1/16"
1.4 mm	1.40	0.0551	≈ 1/16"
1.5 mm	1.50	0.0591	≈ 1/16"
#53	1.51	0.0595	≈ 1/16"
1/16"	1.59	0.0625	1/16"
1.6 mm	1.60	0.0630	1/16"	M2 coarse tap drill
#52	1.61	0.0635	≈ 1/16"
1.7 mm	1.70	0.0669	≈ 1/16"
#51	1.70	0.0670	≈ 1/16"
#50	1.78	0.0700	≈ 1/16"
1.8 mm	1.80	0.0709	≈ 5/64"
#49	1.85	0.0730	≈ 5/64"
1.9 mm	1.90	0.0748	≈ 5/64"
#48	1.93	0.0760	≈ 5/64"
5/64"	1.98	0.0781	5/64"
#47	1.99	0.0785	5/64"
2 mm	2.00	0.0787	≈ 5/64"
2.05 mm	2.05	0.0807	≈ 5/64"	M2.5 coarse tap drill
#46	2.06	0.0810	≈ 5/64"
#45	2.08	0.0820	≈ 5/64"
2.1 mm	2.10	0.0827	≈ 5/64"
#44	2.18	0.0860	≈ 3/32"
2.2 mm	2.20	0.0866	≈ 3/32"
#43	2.26	0.0890	≈ 3/32"	4-40 UNC tap drill
2.3 mm	2.30	0.0906	≈ 3/32"
#42	2.37	0.0935	3/32"
3/32"	2.38	0.0938	3/32"
2.4 mm	2.40	0.0945	≈ 3/32"	M2 clearance hole
#41	2.44	0.0960	≈ 3/32"
#40	2.49	0.0980	≈ 3/32"
2.5 mm	2.50	0.0984	≈ 3/32"	M3 coarse tap drill
#39	2.53	0.0995	≈ 3/32"
#38	2.58	0.1015	≈ 3/32"
2.6 mm	2.60	0.1024	≈ 7/64"
#37	2.64	0.1040	≈ 7/64"
2.7 mm	2.70	0.1063	≈ 7/64"
#36	2.71	0.1065	≈ 7/64"	6-32 UNC tap drill
7/64"	2.78	0.1094	7/64"
#35	2.79	0.1100	≈ 7/64"
2.8 mm	2.80	0.1102	≈ 7/64"
#34	2.82	0.1110	≈ 7/64"
#33	2.87	0.1130	≈ 7/64"
2.9 mm	2.90	0.1142	≈ 7/64"	M2.5 clearance hole
#32	2.95	0.1160	≈ 7/64"
3 mm	3.00	0.1181	≈ 1/8"
#31	3.05	0.1200	≈ 1/8"
3.1 mm	3.10	0.1220	≈ 1/8"
1/8"	3.17	0.1250	1/8"
3.2 mm	3.20	0.1260	≈ 1/8"
#30	3.26	0.1285	≈ 1/8"
3.3 mm	3.30	0.1299	≈ 1/8"	M4 coarse tap drill
3.4 mm	3.40	0.1339	≈ 9/64"	M3 clearance hole
#29	3.45	0.1360	≈ 9/64"	8-32 UNC tap drill
3.5 mm	3.50	0.1378	≈ 9/64"
#28	3.57	0.1405	9/64"
9/64"	3.57	0.1406	9/64"
3.6 mm	3.60	0.1417	≈ 9/64"
#27	3.66	0.1440	≈ 9/64"
3.7 mm	3.70	0.1457	≈ 9/64"
#26	3.73	0.1470	≈ 9/64"
#25	3.80	0.1495	≈ 5/32"	10-24 UNC tap drill
3.8 mm	3.80	0.1496	≈ 5/32"
#24	3.86	0.1520	≈ 5/32"
3.9 mm	3.90	0.1535	≈ 5/32"
#23	3.91	0.1540	≈ 5/32"
5/32"	3.97	0.1563	5/32"
#22	3.99	0.1570	≈ 5/32"
4 mm	4.00	0.1575	≈ 5/32"
#21	4.04	0.1590	≈ 5/32"	10-32 UNF tap drill
#20	4.09	0.1610	≈ 5/32"
4.1 mm	4.10	0.1614	≈ 5/32"
4.2 mm	4.20	0.1654	≈ 11/64"	M5 coarse tap drill
#19	4.22	0.1660	≈ 11/64"
4.3 mm	4.30	0.1693	≈ 11/64"
#18	4.31	0.1695	≈ 11/64"
11/64"	4.37	0.1719	11/64"
#17	4.39	0.1730	≈ 11/64"
4.4 mm	4.40	0.1732	≈ 11/64"
#16	4.50	0.1770	≈ 11/64"
4.5 mm	4.50	0.1772	≈ 11/64"	M4 clearance hole
#15	4.57	0.1800	≈ 3/16"
4.6 mm	4.60	0.1811	≈ 3/16"
#14	4.62	0.1820	≈ 3/16"
#13	4.70	0.1850	≈ 3/16"
4.7 mm	4.70	0.1850	≈ 3/16"
3/16"	4.76	0.1875	3/16"
4.8 mm	4.80	0.1890	≈ 3/16"
#12	4.80	0.1890	≈ 3/16"
#11	4.85	0.1910	≈ 3/16"	Rivet hole for 3/16" rivets
4.9 mm	4.90	0.1929	≈ 3/16"
#10	4.91	0.1935	≈ 3/16"
#9	4.98	0.1960	≈ 13/64"
5 mm	5.00	0.1969	≈ 13/64"	M6 coarse tap drill · yellow wall plug
#8	5.05	0.1990	≈ 13/64"
5.1 mm	5.10	0.2008	≈ 13/64"
#7	5.11	0.2010	≈ 13/64"	1/4-20 UNC tap drill
13/64"	5.16	0.2031	13/64"
#6	5.18	0.2040	≈ 13/64"
5.2 mm	5.20	0.2047	≈ 13/64"
#5	5.22	0.2055	≈ 13/64"
5.3 mm	5.30	0.2087	≈ 13/64"
#4	5.31	0.2090	≈ 13/64"
5.4 mm	5.40	0.2126	≈ 7/32"
#3	5.41	0.2130	≈ 7/32"	1/4-28 UNF tap drill
5.5 mm	5.50	0.2165	≈ 7/32"	M5 clearance hole
7/32"	5.56	0.2188	7/32"
5.6 mm	5.60	0.2205	≈ 7/32"
#2	5.61	0.2210	≈ 7/32"
5.7 mm	5.70	0.2244	≈ 7/32"
#1	5.79	0.2280	≈ 15/64"
5.8 mm	5.80	0.2283	≈ 15/64"
5.9 mm	5.90	0.2323	≈ 15/64"
A	5.94	0.2340	15/64"
15/64"	5.95	0.2344	15/64"
6 mm	6.00	0.2362	≈ 15/64"	Red wall plug · M7 tap drill
B	6.05	0.2380	≈ 15/64"
6.1 mm	6.10	0.2402	≈ 15/64"
C	6.15	0.2420	≈ 15/64"
6.2 mm	6.20	0.2441	≈ 1/4"
D	6.25	0.2460	≈ 1/4"
6.3 mm	6.30	0.2480	≈ 1/4"
1/4"	6.35	0.2500	1/4"
E	6.35	0.2500	1/4"
6.4 mm	6.40	0.2520	≈ 1/4"
6.5 mm	6.50	0.2559	≈ 1/4"
F	6.53	0.2570	≈ 1/4"	5/16-18 UNC tap drill
6.6 mm	6.60	0.2598	≈ 17/64"	M6 clearance hole
G	6.63	0.2610	≈ 17/64"
6.7 mm	6.70	0.2638	≈ 17/64"
17/64"	6.75	0.2656	17/64"
6.75 mm	6.75	0.2657	17/64"
H	6.76	0.2660	17/64"
6.8 mm	6.80	0.2677	≈ 17/64"	M8 coarse tap drill
6.9 mm	6.90	0.2717	≈ 17/64"
I	6.91	0.2720	≈ 17/64"	5/16-24 UNF tap drill
7 mm	7.00	0.2756	≈ 9/32"	Brown wall plug
J	7.04	0.2770	≈ 9/32"
7.1 mm	7.10	0.2795	≈ 9/32"
K	7.14	0.2810	9/32"
9/32"	7.14	0.2813	9/32"
7.2 mm	7.20	0.2835	≈ 9/32"
7.3 mm	7.30	0.2874	≈ 9/32"
L	7.37	0.2900	≈ 19/64"
7.4 mm	7.40	0.2913	≈ 19/64"
M	7.49	0.2950	≈ 19/64"
7.5 mm	7.50	0.2953	≈ 19/64"
19/64"	7.54	0.2969	19/64"
7.6 mm	7.60	0.2992	≈ 19/64"
N	7.67	0.3020	≈ 19/64"
7.7 mm	7.70	0.3031	≈ 19/64"
7.8 mm	7.80	0.3071	≈ 5/16"
7.9 mm	7.90	0.3110	≈ 5/16"
5/16"	7.94	0.3125	5/16"	3/8-16 UNC tap drill
8 mm	8.00	0.3150	≈ 5/16"
O	8.03	0.3160	≈ 5/16"
8.1 mm	8.10	0.3189	≈ 5/16"
8.2 mm	8.20	0.3228	≈ 21/64"
P	8.20	0.3230	≈ 21/64"
8.3 mm	8.30	0.3268	≈ 21/64"
21/64"	8.33	0.3281	21/64"
8.4 mm	8.40	0.3307	≈ 21/64"
Q	8.43	0.3320	≈ 21/64"	3/8-24 UNF tap drill
8.5 mm	8.50	0.3346	≈ 21/64"	M10 coarse tap drill
8.6 mm	8.60	0.3386	≈ 11/32"
R	8.61	0.3390	≈ 11/32"
8.7 mm	8.70	0.3425	≈ 11/32"
11/32"	8.73	0.3438	11/32"
8.8 mm	8.80	0.3465	≈ 11/32"
S	8.84	0.3480	≈ 11/32"
8.9 mm	8.90	0.3504	≈ 11/32"
9 mm	9.00	0.3543	≈ 23/64"	M8 clearance hole
T	9.09	0.3580	≈ 23/64"
9.1 mm	9.10	0.3583	≈ 23/64"
23/64"	9.13	0.3594	23/64"
9.2 mm	9.20	0.3622	≈ 23/64"
9.3 mm	9.30	0.3661	≈ 23/64"
U	9.35	0.3680	≈ 3/8"	7/16-14 UNC tap drill
9.4 mm	9.40	0.3701	≈ 3/8"
9.5 mm	9.50	0.3740	≈ 3/8"
3/8"	9.52	0.3750	3/8"
V	9.58	0.3770	≈ 3/8"
9.6 mm	9.60	0.3780	≈ 3/8"
9.7 mm	9.70	0.3819	≈ 3/8"
9.8 mm	9.80	0.3858	≈ 25/64"
W	9.80	0.3860	≈ 25/64"
9.9 mm	9.90	0.3898	≈ 25/64"
25/64"	9.92	0.3906	25/64"	7/16-20 UNF tap drill
10 mm	10.00	0.3937	≈ 25/64"	Blue wall plug
X	10.08	0.3970	≈ 25/64"
10.1 mm	10.10	0.3976	≈ 25/64"
10.2 mm	10.20	0.4016	≈ 13/32"	M12 coarse tap drill
10.25 mm	10.25	0.4035	≈ 13/32"
Y	10.26	0.4040	≈ 13/32"
10.3 mm	10.30	0.4055	≈ 13/32"
13/32"	10.32	0.4063	13/32"
10.4 mm	10.40	0.4094	≈ 13/32"
Z	10.49	0.4130	≈ 13/32"
10.5 mm	10.50	0.4134	≈ 13/32"
10.6 mm	10.60	0.4173	≈ 27/64"
10.7 mm	10.70	0.4213	≈ 27/64"
27/64"	10.72	0.4219	27/64"	1/2-13 UNC tap drill
10.8 mm	10.80	0.4252	≈ 27/64"
10.9 mm	10.90	0.4291	≈ 27/64"
11 mm	11.00	0.4331	≈ 7/16"	M10 clearance hole
11.1 mm	11.10	0.4370	7/16"
7/16"	11.11	0.4375	7/16"
11.2 mm	11.20	0.4409	≈ 7/16"
11.3 mm	11.30	0.4449	≈ 7/16"
11.4 mm	11.40	0.4488	≈ 29/64"
11.5 mm	11.50	0.4528	29/64"
29/64"	11.51	0.4531	29/64"	1/2-20 UNF tap drill
11.6 mm	11.60	0.4567	≈ 29/64"
11.7 mm	11.70	0.4606	≈ 29/64"
11.8 mm	11.80	0.4646	≈ 15/32"
11.9 mm	11.90	0.4685	15/32"
15/32"	11.91	0.4688	15/32"
12 mm	12.00	0.4724	≈ 15/32"	M14 coarse tap drill
12.1 mm	12.10	0.4764	≈ 15/32"
12.2 mm	12.20	0.4803	≈ 31/64"
12.3 mm	12.30	0.4843	31/64"
31/64"	12.30	0.4844	31/64"
12.4 mm	12.40	0.4882	≈ 31/64"
12.5 mm	12.50	0.4921	≈ 31/64"
12.6 mm	12.60	0.4961	≈ 1/2"
12.7 mm	12.70	0.5000	1/2"
1/2"	12.70	0.5000	1/2"
12.8 mm	12.80	0.5039	≈ 1/2"
12.9 mm	12.90	0.5079	≈ 33/64"
13 mm	13.00	0.5118	≈ 33/64"	M12 clearance hole
33/64"	13.10	0.5156	33/64"
17/32"	13.49	0.5313	17/32"	5/8-11 UNC tap drill
35/64"	13.89	0.5469	35/64"
9/16"	14.29	0.5625	9/16"
37/64"	14.68	0.5781	37/64"
19/32"	15.08	0.5938	19/32"
39/64"	15.48	0.6094	39/64"
5/8"	15.88	0.6250	5/8"
41/64"	16.27	0.6406	41/64"
21/32"	16.67	0.6563	21/32"	3/4-10 UNC tap drill
43/64"	17.07	0.6719	43/64"
11/16"	17.46	0.6875	11/16"
45/64"	17.86	0.7031	45/64"
23/32"	18.26	0.7188	23/32"
47/64"	18.65	0.7344	47/64"
3/4"	19.05	0.7500	3/4"
49/64"	19.45	0.7656	49/64"
25/32"	19.84	0.7813	25/32"
51/64"	20.24	0.7969	51/64"
13/16"	20.64	0.8125	13/16"
53/64"	21.03	0.8281	53/64"
27/32"	21.43	0.8438	27/32"
55/64"	21.83	0.8594	55/64"
7/8"	22.22	0.8750	7/8"	1-8 UNC tap drill
57/64"	22.62	0.8906	57/64"
29/32"	23.02	0.9063	29/32"
59/64"	23.42	0.9219	59/64"
15/16"	23.81	0.9375	15/16"
61/64"	24.21	0.9531	61/64"
31/32"	24.61	0.9688	31/32"
63/64"	25.00	0.9844	63/64"
1/1"	25.40	1.0000	1/1"

Common questions

What size is a #11 drill bit in mm?+

A #11 drill bit is 0.1910 inch, which is 4.85 mm. Order a 4.9 mm bit as the metric substitute. Its classic use is the hole for a 3/16 inch rivet.

What is 6.8 mm in inches?+

6.8 mm is 0.2677 inch, closest to 17/64". It is best known as the tap drill for an M8 coarse thread, which is why it wears out faster than the sizes either side of it.

Is 6 mm the same as 1/4 inch?+

No. 1/4 inch is 6.35 mm, so a 6 mm bit is 0.35 mm undersize — enough that a 1/4 inch bolt will not pass through the hole. Use 6.4 mm or 6.5 mm for a 1/4 inch clearance hole.

Can I substitute a metric bit for a gauge drill?+

Usually yes. For tap drills round up, never down — an undersized tap drill is the most common reason taps snap. For clearance holes stay within about +0.2 mm. For reamed or dowel holes, do not substitute at all.

How do I measure a drill bit with no markings?+

Measure across the two margins just behind the point with a caliper — not on the shank, which may be reduced, and not down the flute, which is relieved and reads undersize. Round up to the nearest catalogue size.