Reference chart

Drill Bit Size Chart: Bit Sizes & Diameters

Look up drill bit sizes with numeric, letter, and fractional drills. Drill diameter in millimeters and inches for CNC programming, drill charts, and tap drill selection.

Size	Diameter (mm)	Diameter (in)	Category
#80	0.34 mm	0.0135″	Numeric
#79	0.37 mm	0.0145″	Numeric
1/64	0.40 mm	0.0156″	Fractional
#78	0.41 mm	0.016″	Numeric
#77	0.46 mm	0.018″	Numeric
#76	0.51 mm	0.02″	Numeric
#75	0.53 mm	0.021″	Numeric
#74	0.57 mm	0.0225″	Numeric
#73	0.61 mm	0.024″	Numeric
#72	0.64 mm	0.025″	Numeric
#71	0.66 mm	0.026″	Numeric
#70	0.71 mm	0.028″	Numeric
#69	0.74 mm	0.0292″	Numeric
#68	0.79 mm	0.031″	Numeric
2/64	0.79 mm	0.0313″	Fractional
#67	0.81 mm	0.032″	Numeric
#66	0.84 mm	0.033″	Numeric
#65	0.89 mm	0.035″	Numeric
#64	0.91 mm	0.036″	Numeric
#63	0.94 mm	0.037″	Numeric
#62	0.97 mm	0.038″	Numeric
#61	0.99 mm	0.039″	Numeric
#60	1.02 mm	0.04″	Numeric
#59	1.04 mm	0.041″	Numeric
#58	1.07 mm	0.042″	Numeric
#57	1.09 mm	0.043″	Numeric
#56	1.18 mm	0.0465″	Numeric
3/64	1.19 mm	0.0469″	Fractional
#55	1.32 mm	0.052″	Numeric
#54	1.40 mm	0.055″	Numeric
#53	1.51 mm	0.0595″	Numeric
4/64	1.59 mm	0.0625″	Fractional
#52	1.61 mm	0.0635″	Numeric
#51	1.70 mm	0.067″	Numeric
#50	1.78 mm	0.07″	Numeric
#49	1.85 mm	0.073″	Numeric
#48	1.93 mm	0.076″	Numeric
5/64	1.98 mm	0.0781″	Fractional
#47	1.99 mm	0.0785″	Numeric
#46	2.06 mm	0.081″	Numeric
#45	2.08 mm	0.082″	Numeric
#44	2.18 mm	0.086″	Numeric
#43	2.26 mm	0.089″	Numeric
#42	2.37 mm	0.0935″	Numeric
6/64	2.38 mm	0.0938″	Fractional
#41	2.44 mm	0.096″	Numeric
#40	2.49 mm	0.098″	Numeric
#39	2.53 mm	0.0995″	Numeric
#38	2.58 mm	0.1015″	Numeric
#37	2.64 mm	0.104″	Numeric
#36	2.71 mm	0.1065″	Numeric
7/64	2.78 mm	0.1094″	Fractional
#35	2.79 mm	0.11″	Numeric
#34	2.82 mm	0.111″	Numeric
#33	2.87 mm	0.113″	Numeric
#32	2.95 mm	0.116″	Numeric
#31	3.05 mm	0.12″	Numeric
8/64	3.17 mm	0.125″	Fractional
#30	3.26 mm	0.1285″	Numeric
#29	3.45 mm	0.136″	Numeric
#28	3.57 mm	0.1405″	Numeric
9/64	3.57 mm	0.1406″	Fractional
#27	3.66 mm	0.144″	Numeric
#26	3.73 mm	0.147″	Numeric
#25	3.80 mm	0.1495″	Numeric
#24	3.86 mm	0.152″	Numeric
#23	3.91 mm	0.154″	Numeric
10/64	3.97 mm	0.1563″	Fractional
#22	3.99 mm	0.157″	Numeric
#21	4.04 mm	0.159″	Numeric
#20	4.09 mm	0.161″	Numeric
#19	4.22 mm	0.166″	Numeric
#18	4.31 mm	0.1695″	Numeric
11/64	4.37 mm	0.1719″	Fractional
#17	4.39 mm	0.173″	Numeric
#16	4.50 mm	0.177″	Numeric
#15	4.57 mm	0.18″	Numeric
#14	4.62 mm	0.182″	Numeric
#13	4.70 mm	0.185″	Numeric
12/64	4.76 mm	0.1875″	Fractional
#12	4.80 mm	0.189″	Numeric
#11	4.85 mm	0.191″	Numeric
#10	4.91 mm	0.1935″	Numeric
#9	4.98 mm	0.196″	Numeric
#8	5.05 mm	0.199″	Numeric
#7	5.11 mm	0.201″	Numeric
13/64	5.16 mm	0.2031″	Fractional
#6	5.18 mm	0.204″	Numeric
#5	5.22 mm	0.2055″	Numeric
#4	5.31 mm	0.209″	Numeric
#3	5.41 mm	0.213″	Numeric
14/64	5.56 mm	0.2188″	Fractional
#2	5.61 mm	0.221″	Numeric
#1	5.79 mm	0.228″	Numeric
A	5.94 mm	0.234″	Letter
15/64	5.95 mm	0.2344″	Fractional
B	6.05 mm	0.238″	Letter
C	6.15 mm	0.242″	Letter
D	6.25 mm	0.246″	Letter
E	6.35 mm	0.25″	Letter
16/64	6.35 mm	0.25″	Fractional
F	6.53 mm	0.257″	Letter
G	6.63 mm	0.261″	Letter
17/64	6.75 mm	0.2656″	Fractional
H	6.76 mm	0.266″	Letter
I	6.91 mm	0.272″	Letter
J	7.04 mm	0.277″	Letter
K	7.14 mm	0.281″	Letter
18/64	7.14 mm	0.2813″	Fractional
L	7.37 mm	0.29″	Letter
M	7.49 mm	0.295″	Letter
19/64	7.54 mm	0.2969″	Fractional
N	7.67 mm	0.302″	Letter
20/64	7.94 mm	0.3125″	Fractional
O	8.03 mm	0.316″	Letter
P	8.20 mm	0.323″	Letter
21/64	8.33 mm	0.3281″	Fractional
Q	8.43 mm	0.332″	Letter
R	8.61 mm	0.339″	Letter
22/64	8.73 mm	0.3438″	Fractional
S	8.84 mm	0.348″	Letter
T	9.09 mm	0.358″	Letter
23/64	9.13 mm	0.3594″	Fractional
U	9.35 mm	0.368″	Letter
24/64	9.52 mm	0.375″	Fractional
V	9.58 mm	0.377″	Letter
W	9.80 mm	0.386″	Letter
25/64	9.92 mm	0.3906″	Fractional
X	10.08 mm	0.397″	Letter
Y	10.26 mm	0.404″	Letter
26/64	10.32 mm	0.4063″	Fractional
Z	10.49 mm	0.413″	Letter
27/64	10.72 mm	0.4219″	Fractional
28/64	11.11 mm	0.4375″	Fractional
29/64	11.51 mm	0.4531″	Fractional
30/64	11.91 mm	0.4688″	Fractional
31/64	12.30 mm	0.4844″	Fractional
32/64	12.70 mm	0.5″	Fractional
33/64	13.10 mm	0.5156″	Fractional
34/64	13.49 mm	0.5313″	Fractional
35/64	13.89 mm	0.5469″	Fractional
36/64	14.29 mm	0.5625″	Fractional
37/64	14.68 mm	0.5781″	Fractional
38/64	15.08 mm	0.5938″	Fractional
39/64	15.48 mm	0.6094″	Fractional
40/64	15.88 mm	0.625″	Fractional
41/64	16.27 mm	0.6406″	Fractional
42/64	16.67 mm	0.6563″	Fractional
43/64	17.07 mm	0.6719″	Fractional
44/64	17.46 mm	0.6875″	Fractional
45/64	17.86 mm	0.7031″	Fractional
46/64	18.26 mm	0.7188″	Fractional
47/64	18.65 mm	0.7344″	Fractional
48/64	19.05 mm	0.75″	Fractional
49/64	19.45 mm	0.7656″	Fractional
50/64	19.84 mm	0.7813″	Fractional
51/64	20.24 mm	0.7969″	Fractional
52/64	20.64 mm	0.8125″	Fractional
53/64	21.03 mm	0.8281″	Fractional
54/64	21.43 mm	0.8438″	Fractional
55/64	21.83 mm	0.8594″	Fractional
56/64	22.22 mm	0.875″	Fractional
57/64	22.62 mm	0.8906″	Fractional
58/64	23.02 mm	0.9063″	Fractional
59/64	23.42 mm	0.9219″	Fractional
60/64	23.81 mm	0.9375″	Fractional
61/64	24.21 mm	0.9531″	Fractional
62/64	24.61 mm	0.9688″	Fractional
63/64	25.00 mm	0.9844″	Fractional
1	25.40 mm	1″	Fractional

Drill size chart for CNC, shop reference, and tap drills

A reliable drill size chart prevents costly mistakes: wrong drill diameter overloads taps, weakens threads, and breaks CAM prove-out cycles.

This drill bit size chart lists numeric, letter, and fractional drill sizes with drill diameter in mm and inches—a single reference for programmers, quoting, and shop-floor drill charts.

Drill series in this drill size chart:

Numeric drills (#80–#1, smallest to largest)
Letter drills (A–Z)
Fractional inch drills (1/64″–1″)

Filter by Numeric, Letter, Fractional, or All. Each row shows size, drill diameter in mm and in, and category—ready to cross-check with tap drill recommendations.

Why a standard drill size chart matters

CNC posts, presetters, and inspection reports assume recognized drill names—not arbitrary decimals.

Accurate drill selection from a drill size chart affects:

Tap drill quality when paired with the correct pre-tap hole
Reamer and bore fit when drilling is a prelude to finishing
Tool life and cycle time in production drilling
First-article inspection and SPC repeatability
Communication between design, CAM, and the shop floor

Keeping numeric, letter, and fractional sizes in one drill bit size chart cuts back-and-forth when a drawing calls out a wire size and programming needs the metric equivalent.

Common uses for this drill size chart

Engineers and machinists use a drill size chart to:

Program drill cycles and CNC tool lists
Look up drill diameter in mm or inches
Cross-check tap drill and thread hole recommendations
Build standard tool libraries
Quote and plan CNC hole operations
Shop-floor drill chart reference

For threaded holes, pair this drill size chart with our Tap Drill Size Calculator. For hole and thread DFM, see the CNC Design Guide.

Notes on this drill size chart

Numeric drill sizes run from #80 (smallest) to #1 (largest). This table lists the full series sorted smallest to largest.
Letter drill sizes run from A (smallest) through Z (largest) and fill gaps between fractional and numeric ranges.
Fractional drill sizes (1/64″ through 1″) are the most common in general machining and standard drill charts.
For tap drill selection, cross-reference this drill size chart with our Tap Drill Size Calculator—not every drill diameter is a valid pre-tap hole.
Always confirm drill diameter against your drawing, material, and the exact tool in your CNC program.

FAQ

Drill size chart questions

A number drill uses the # series from #80 (smallest, about 0.0135″) to #1 (largest, about 0.228″). Number drills fill gaps between fractional sizes and appear in standard drill size charts and tap drill tables.

Letter drills (A–Z) cover mid-range diameters when a fractional size is too small. Number drills extend finer and coarser. Both are listed in this drill bit size chart with drill diameter in mm and inches.

Multiply the decimal inch value by 25.4, or use the Diameter (mm) column in this drill size chart directly—no manual conversion needed during programming or inspection.

Use a tap drill chart or calculator, not the bolt clearance size. The correct pre-tap hole depends on thread series, pitch, and tap type. See our Tap Drill Size Calculator.

No. Fractional drills use common inch fractions (1/64, 1/32, etc.). Number and letter drills use separate naming systems. Shops reference all three in one drill size chart.

Published values are nominal catalog diameters. Actual drill diameter can vary with brand, wear, runout, and material. For tight tolerances, measure the tool or verify on a test piece.

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Size

Diameter (mm)

Diameter (in)