Drill Speed Calculator (Drill Press RPM for Wood and Metal)

Run a drill too fast and the corners of the bit burn off; run it too slowly in a soft material and it grabs, tears and wastes time. This calculator gives the spindle speed for a twist drill from the cutting speeds published in the US Army’s machine tool manual, TC 9-524 Fundamentals of Machine Tools (Table 4-2, high speed steel drills). Pick the material, enter the drill diameter and it returns the speed to start at, the full range for that material, the point angle and the coolant the manual lists. Below it is a drill press speed chart for common sizes.

Drill speed calculator

How it works

Every material has a cutting speed: how fast the outside corner of the drill may travel through it, in surface feet per minute (or metres per minute). The spindle speed follows from the circumference of the drill:

RPM = 12 × cutting speed (ft/min) ÷ (π × drill diameter in inches) = 3.82 × CS ÷ D
Metric: RPM = 1,000 × cutting speed (m/min) ÷ (π × drill diameter in mm) = 318 × CS ÷ D

TC 9-524 rounds the constants to 4 and 320 so the sum can be done in your head; the calculator shows that shop figure too, and it comes out about 5% faster. The manual says to use the slower of the two cutting speeds it lists for a material, because rigidity of the setup, the size of the machine and the finish you want all vary. That is the figure in the first row; go towards the top of the range only if the drill is cutting cleanly and staying cool.

Worked example

A 1/2 in high speed steel drill through a mild steel bracket (low carbon steel, cutting speed 80 to 110 ft/min):

Units: Inches
Material: Steel, low carbon (0.2 to 0.3% C, mild steel)
Drill diameter: 0.5 in

The calculator gives:

Drill speed (start here): 611 RPM
Range for this material: 611 to 840 RPM
Cutting speed used: 80 to 110 ft/min (surface feet per minute)
Shop rule of thumb (CS x 4 / D): 640 RPM
Drill point angle: 110 to 118 degrees
Coolant: soap solution

Start at about 611 RPM, or the nearest step your drill press has. The manual’s own worked example is a 1/2 in drill in aluminium at 200 ft/min: 200 × 4 ÷ 0.5 = 1,600 RPM with the shortcut, or 1,528 RPM with π. For the same hole in free-machining stainless the starting speed drops to about 229 RPM, a quarter of the mild steel figure.

Drill press speed chart (RPM, high speed steel drills)

Drill	Wood	Aluminium	Brass	Soft cast iron	Mild steel	Alloy steel	Stainless (free machining)
1/16 in	18,330	12,220	12,220	6,110	4,890	3,060	1,830
1/8 in	9,170	6,110	6,110	3,060	2,440	1,530	920
3/16 in	6,110	4,070	4,070	2,040	1,630	1,020	610
1/4 in	4,580	3,060	3,060	1,530	1,220	760	460
5/16 in	3,670	2,440	2,440	1,220	980	610	370
3/8 in	3,060	2,040	2,040	1,020	810	510	310
7/16 in	2,620	1,750	1,750	870	700	440	260
1/2 in	2,290	1,530	1,530	760	610	380	230
5/8 in	1,830	1,220	1,220	610	490	310	180
3/4 in	1,530	1,020	1,020	510	410	250	150
7/8 in	1,310	870	870	440	350	220	130
1 in	1,150	760	760	380	310	190	110

Lower end of the TC 9-524 Table 4-2 cutting speed for each material (wood 300, aluminium and brass 200, soft cast iron 100, mild steel 80, alloy steel 50, free-machining stainless 30 ft/min), rounded to the nearest 10 RPM.

Metric drill speed chart (RPM)

Drill	Wood	Aluminium	Brass	Soft cast iron	Mild steel	Alloy steel	Stainless (free machining)
3 mm	9,710	6,470	6,470	3,240	2,590	1,620	970
4 mm	7,280	4,850	4,850	2,430	1,940	1,210	730
5 mm	5,830	3,880	3,880	1,940	1,550	970	580
6 mm	4,850	3,240	3,240	1,620	1,290	810	490
8 mm	3,640	2,430	2,430	1,210	970	610	360
10 mm	2,910	1,940	1,940	970	780	490	290
12 mm	2,430	1,620	1,620	810	650	400	240
14 mm	2,080	1,390	1,390	690	550	350	210
16 mm	1,820	1,210	1,210	610	490	300	180
20 mm	1,460	970	970	490	390	240	150
25 mm	1,170	780	780	390	310	190	120

Same table in millimetres, from the metric cutting speeds in Table 4-2 (wood 91.5, aluminium 61, mild steel 24.4 m/min and so on).

Notes and limits

Speeds are for high speed steel twist drills, the drills the manual’s table covers. For carbon steel, cobalt or carbide drills use the drill maker’s figures.
Feed matters as much as speed. In steel you want a continuous curl of chip, not dust and not a screech. If the drill squeals or the chip turns blue, slow the spindle and keep the feed steady.
Wood is listed at 300 to 400 ft/min with a 60 to 70 degree point, dry. Brad-point bits, with their centre spur, usually leave a cleaner hole in wood than a metalworking point.
Large wood bits are a different case: Forstner bits, spade bits, hole saws and circle cutters carry their own speed limits, much lower than a twist drill of the same size. Use those.
Drill size charts and the drill for each tap are in the drill bit size chart and the tap drill calculator.

Frequently asked questions

What speed should I drill a 1/4 inch hole in steel?

About 1,220 RPM in mild (low carbon) steel with a high speed steel drill, from 80 ft/min. In alloy steel start near 760 RPM, and in free-machining stainless near 460 RPM.

What drill press speed for wood?

For a twist or brad-point drill, about 4,580 RPM at 1/4 in and 2,290 RPM at 1/2 in, from the manual’s 300 ft/min for wood. Most drill presses top out below that for small bits, so use the top speed. Forstner bits and hole saws need much slower speeds set by their makers.

How fast should I drill aluminium?

About 3,060 RPM for a 1/4 in drill and 1,530 RPM for a 1/2 in drill, from the lower 200 ft/min figure, with kerosene or soluble oil as the lubricant.

Why does a bigger drill need a slower speed?

The outside of a large drill travels further each turn. A 1 in drill at 600 RPM moves its corners as fast as a 1/2 in drill at 1,200 RPM, so to keep the cutting speed the same the spindle has to turn more slowly as the diameter goes up.

What is the formula for drill RPM?

RPM = 12 × cutting speed in ft/min ÷ (π × diameter in inches), about 3.82 × CS ÷ D. The shop shortcut in TC 9-524 is CS × 4 ÷ D; in metric, CS in m/min × 320 ÷ D in mm.

Sources

Last reviewed: 25 October 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.