Drill size chart – inch and metric | Downloadable PDF

Every drill size chart you’ll ever need is in this article! No more scratching your head wondering which gauge relates to which size or how to convert inches to mm or vice versa. This is your one-stop-shop for all drill bit size conversions and tables.

But, there’s more to this article than just charts.

You will also get some background on how the various drill sizes came about, how they are calculated and some of their applications. If you’ve ever wondered why there are so many different gauge designations and drill bit sizes, then read on.

How to Measure Drill Bits

To measure the diameter of a drill bit, it’s best to measure the cutting edge rather than the shank (the shank is the part that is held by the drill chuck). To get an accurate measurement, use Vernier callipers, but be aware that depending on the quality of the drill bit, there could be a tolerance error of between 5 and 15 thousandths of a unit.

Metric Drill Bit Sizes

Metric drill sizes are used primarily in Europe and use metric units to measure the drill bit diameter. There are a variety of standards used to define drill sizes, the most common one in the UK is the British Standard BS 328 set which includes twist drill bit sizes between 0.2 mm and 25 mm.

BS 328 drill sizes are defined as shown in the drill size chart below:

ø0.2 to 0.98 mm:	N. 0.1 mm N. 0.1 + 0.02 mm N. 0.1 + 0.05 mm N. 0.1 + 0.08 mm	N is an integer between 2 and 9
ø1.0 to 2.95 mm:	N. 0.1 mm N. 0.1 + 0.05 mm	N is an integer between 10 and 29
ø3.0 to 13.9 mm:	N. 0.1 mm	N is an integer between 30 and 139
ø14.0 to 25.0 mm:	M. 1mm M. 1 + 0.25 mm M. 1 + 0.5 mm M. 1 + 0.75 mm	M is an integer between 14 to 25

Please note that BS 328 sizing only applies to twist drill bits. Other bit types, such as Forstner bits, will contain different size cutting surfaces.

Another example of a metric set of drill sizes is the Renard series, which uses a simple factor to determine the diameter:

• The R5 series uses a factor of 1.58 and contains the following sizes: M2.5, M4, M6, M10, M16 and M24
• The R10 series uses a factor of 1.26 and contains the following sizes: M3, M5, M8, M12, M20 and M30

Drill Size Chart for Number and Letter Gauges

Number and letter gauges do not follow a formula or standard increments. They are loosely based on the Stubs Steel Wire Gauge, with gauge sizes that are similar (but not entirely identical) to that system.

Although they originated in the 19^thcentury, these gauges are still commonly used in the U.S. They are also seen in the UK to a lesser degree, having been largely replaced by metric sizes. Most other countries, especially in Europe, have abandoned them entirely in favour of metric systems.

The drill size chart below contains imperial and metric drill bit diameter measurements for all number and letter gauges.

Gauge	inch	mm		Gauge	inch	mm		Gauge	inch	mm
104	0.0031	0.079		52	0.0635	1.613		A	0.234	5.944
103	0.0035	0.089		51	0.067	1.702		B	0.238	6.045
102	0.0039	0.099		50	0.07	1.778		C	0.242	6.147
101	0.0043	0.109		49	0.073	1.854		D	0.246	6.248
100	0.0047	0.119		48	0.076	1.93		E	0.25	6.35
99	0.0051	0.13		47	0.0785	1.994		F	0.257	6.528
98	0.0055	0.14		46	0.081	2.057		G	0.261	6.629
97	0.0059	0.15		45	0.082	2.083		H	0.266	6.756
96	0.0063	0.16		44	0.086	2.184		I	0.272	6.909
95	0.0067	0.17		43	0.089	2.261		J	0.277	7.036
94	0.0071	0.18		42	0.0935	2.375		K	0.281	7.137
93	0.0075	0.191		41	0.096	2.438		L	0.29	7.366
92	0.0079	0.201		40	0.098	2.489		M	0.295	7.493
91	0.0083	0.211		39	0.0995	2.527		N	0.302	7.671
90	0.0087	0.221		38	0.1015	2.578		O	0.316	8.026
89	0.0091	0.231		37	0.104	2.642		P	0.323	8.204
88	0.0095	0.241		36	0.1065	2.705		Q	0.332	8.433
87	0.01	0.254		35	0.11	2.794		R	0.339	8.611
86	0.0105	0.267		34	0.111	2.819		S	0.348	8.839
85	0.011	0.279		33	0.113	2.87		T	0.358	9.093
84	0.0115	0.292		32	0.116	2.946		U	0.368	9.347
83	0.012	0.305		31	0.12	3.048		V	0.377	9.576
82	0.0125	0.318		30	0.1285	3.264		W	0.386	9.804
81	0.013	0.33		29	0.136	3.454		X	0.397	10.08
80	0.0135	0.343		28	0.1405	3.569		Y	0.404	10.26
79	0.0145	0.368		27	0.144	3.658		Z	0.413	10.49
78	0.016	0.406		26	0.147	3.734		R	0.339	8.611
77	0.018	0.457		25	0.1495	3.797		S	0.348	8.839
76	0.02	0.508		24	0.152	3.861		T	0.358	9.093
75	0.021	0.533		23	0.154	3.912		U	0.368	9.347
74	0.0225	0.572		22	0.157	3.988		V	0.377	9.576
73	0.024	0.61		21	0.159	4.039
72	0.025	0.635		20	0.161	4.089
71	0.026	0.66		19	0.166	4.216
70	0.028	0.711		18	0.1695	4.305
69	0.0292	0.742		17	0.173	4.394
68	0.031	0.787		16	0.177	4.496
67	0.032	0.813		15	0.18	4.572
66	0.033	0.838		14	0.182	4.623
65	0.035	0.889		13	0.185	4.699
64	0.036	0.914		12	0.189	4.801
63	0.037	0.94		11	0.191	4.851
62	0.038	0.965		10	0.1935	4.915
61	0.039	0.991		9	0.196	4.978
60	0.04	1.016		8	0.199	5.055
59	0.041	1.041		7	0.201	5.105
58	0.042	1.067		6	0.204	5.182
57	0.043	1.092		5	0.2055	5.22
56	0.0465	1.181		4	0.209	5.309
55	0.052	1.321		3	0.213	5.41
54	0.055	1.397		2	0.221	5.613
53	0.0595	1.511		1	0.228	5.791

Fractional-inch Drill Size Chart

Fractional drill bits are definedby the ANSI B94.11M-1979 standard.

Most commonly used in the US, but can still be found occasionally in the UK, these imperial measurement drill bits come in 1/64 inch increments. The fractions used are always in their simplest form, i.e. reduced as far as possible, so 2/64 becomes 1/32 for instance.

The drill size chart below gives fractional sizes and their metric conversions up to 1 inch.

Fraction of an inch	inch	mm		Fraction of an inch	inch	mm		Fraction of an inch	inch	mm
1/64	0.0156	0.3969		23/64	0.3594	9.1281		45/64	0.7031	17.8594
1/32	0.0313	0.7938		3/8	0.3750	9.5250		23/32	0.7188	18.2563
3/64	0.0469	1.1906		25/64	0.3906	9.9219		47/64	0.7344	18.6531
1/16	0.0625	1.5875		13/32	0.4063	10.3188		3/4	0.7500	19.0500
5/64	0.0781	1.9844		27/64	0.4219	10.7156		49/64	0.7656	19.4469
3/32	0.0938	2.3813		7/16	0.4375	11.1125		25/32	0.7813	19.8438
7/64	0.1094	2.7781		29/64	0.4531	11.5094		51/64	0.7969	20.2406
1/8	0.1250	3.1750		15/32	0.4688	11.9063		13/16	0.8125	20.6375
9/64	0.1406	3.5719		31/64	0.4844	12.3031		53/64	0.8281	21.0344
5/32	0.1563	3.9688		1/2	0.5000	12.7000		27/32	0.8438	21.4313
11/64	0.1719	4.3656		33/64	0.5156	13.0969		55/64	0.8594	21.8281
3/16	0.1875	4.7625		17/32	0.5313	13.4938		7/8	0.8750	22.2250
13/64	0.2031	5.1594		35/64	0.5469	13.8906		57/64	0.8906	22.6219
7/32	0.2188	5.5563		9/16	0.5625	14.2875		29/32	0.9063	23.0188
15/64	0.2344	5.9531		37/64	0.5781	14.6844		59/64	0.9219	23.4156
1/4	0.2500	6.3500		19/32	0.5938	15.0813		15/16	0.9375	23.8125
17/64	0.2656	6.7469		39/64	0.6094	15.4781		61/64	0.9531	24.2094
9/32	0.2813	7.1438		5/8	0.6250	15.8750		31/32	0.9688	24.6063
19/64	0.2969	7.5406		41/64	0.6406	16.2719		63/64	0.9844	25.0031
5/16	0.3125	7.9375		21/32	0.6563	16.6688		1	1.0000	25.4000
21/64	0.3281	8.3344		43/64	0.6719	17.0656
11/32	0.3438	8.7313		11/16	0.6875	17.4625

Centre Drill Bit Sizes

These specialist drill bits are used for drilling centre holes at two different angles, 60 degrees and 90 degrees. They are commonly used to drill lathe centres and spotting drills, i.e.marking holes to guide twist drilling.

The drill size chart below contains all commonly used centre drill bit sizes.

Size designation	Drill diameter [inches (mm)]
5/0	0.010 in (0.254 mm)
4/0	0.015 in (0.381 mm)
3/0	0.020 in (0.508 mm)
2/0	0.025 in (0.635 mm)
0	1/32 in (0.794 mm)
1	3/64 in (1.191 mm)
2	5/64 in (1.984 mm)
3	7/64 in (2.778 mm)
4	1/8 in (3.175 mm)
4½	9/64 in (3.572 mm)
5	3/16 in (4.763 mm)
6	7/32 in (5.556 mm)
7	1/4 in (6.350 mm)
8	5/16 in (7.938 mm)
Gauge	Body diameter [inches (mm)]
BS1	1/8 in (3.175 mm)
BS2	3/16 in (4.763 mm)
BS3	1/4 in (6.350 mm)
BS4	5/16 in (7.938 mm)
BS5	7/16 in (11.113 mm)
BS5A	1/2 in (12.700 mm)
BS6	5/8 in (15.875 mm)
BS7	3/4 in (19.050 mm)

Drill Bit Lengths

The length of drill bits vary depending on their application.

• Jobber-length drill bits are the most common, with a length somewhere between 9 to 14 times the diameter.
• Screw-machine-length drills arethe shortest available standard sized bits. They are used primarily in machinist workshops for screw machinesand are not usually available in hardware stores.
• Aircraft-length drills are extended length drill bits that are manufactured in fixed length such as 4, 6, 8, 12, 18, 24-inch bits, rather than proportional lengths.