Reference Chart

Drill Bit Size Chart

Q: What is the difference between jobber and screw machine length drills?

Jobber length drills are the standard length. They work for most general drilling. Screw machine length drills are shorter and stiffer. They reduce deflection and are better for CNC machines where rigidity matters.

Look up number, letter, and fractional drill bit sizes. Find the diameter in inches and mm for over 40 common drill sizes used in CNC machining.

Size ▲	Diameter (in) ▲	Diameter (mm) ▲	Category ▲
#60	0.0400	1.016	Number
#57	0.0430	1.092	Number
#56	0.0465	1.181	Number
#55	0.0520	1.321	Number
#54	0.0550	1.397	Number
#53	0.0595	1.511	Number
#50	0.0700	1.778	Number
#48	0.0760	1.930	Number
#44	0.0860	2.184	Number
#43	0.0890	2.261	Number
#40	0.0980	2.489	Number
#36	0.1065	2.705	Number
#33	0.1130	2.870	Number
#29	0.1360	3.454	Number
#25	0.1495	3.797	Number
#21	0.1590	4.039	Number
#16	0.1770	4.496	Number
#11	0.1910	4.851	Number
#7	0.2010	5.105	Number
#3	0.2130	5.410	Number
#1	0.2280	5.791	Number
A	0.2340	5.944	Letter
D	0.2460	6.248	Letter
F	0.2570	6.528	Letter
H	0.2660	6.756	Letter
J	0.2770	7.036	Letter
L	0.2900	7.366	Letter
N	0.3020	7.671	Letter
P	0.3230	8.204	Letter
R	0.3390	8.611	Letter
T	0.3580	9.093	Letter
V	0.3770	9.576	Letter
X	0.3970	10.084	Letter
Z	0.4130	10.490	Letter
1/16"	0.0625	1.588	Fractional
3/32"	0.0938	2.381	Fractional
1/8"	0.1250	3.175	Fractional
3/16"	0.1875	4.763	Fractional
1/4"	0.2500	6.350	Fractional
5/16"	0.3125	7.938	Fractional
3/8"	0.3750	9.525	Fractional
1/2"	0.5000	12.700	Fractional
3/4"	0.7500	19.050	Fractional
1"	1.0000	25.400	Fractional

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Notes on This Drill Bit Size Chart

Number drill bits run from #1 (largest) to #80 (smallest). Only key sizes are shown.
Letter drill bits run from A (smallest) to Z (largest).
Fractional drill bit sizes are the most common in general machining.
For tap drill bit sizes, cross-reference this chart with a thread pitch chart.

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Frequently Asked Questions

What are number drill bit sizes?

Number drill bits run from #1 (0.2280 in) to #80 (0.0135 in). A higher number means a smaller drill bit. They fill the gaps between fractional sizes and are common for tap drill holes.

What are letter drill bit sizes?

Letter drill bits run from A (0.234 in) to Z (0.413 in). They fill the gaps between fractional sizes in the mid-range. Letter drill bits are common in machine shops for clearance and tap drill holes.

How do I pick a tap drill bit size?

Look up the thread size you need. Find the recommended tap drill bit in a tap drill chart. The tap drill bit makes a hole slightly smaller than the thread so the tap can cut threads into the wall. A 75% thread depth works for most jobs.

What is the difference between jobber and screw machine length drills?

Jobber length is the standard length. It works for most drilling. Screw machine length is shorter and stiffer. It reduces deflection and works better on CNC machines where rigidity matters.

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Drill Bit Size Chart

Notes on This Drill Bit Size Chart

Frequently Asked Questions

Related Resources

Tap & Drill Size Chart | UNC, UNF & Metric Thread Sizes

Countersink Size Chart | Screw Size to Hole & Angle Reference

End Mill Size Chart | Diameters, Flutes & Shank Sizes

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