Workshop and Metalwork Calculators
Drill speed.
Choose the material and the bit diameter. You get a spindle speed range in RPM from published cutting speeds, so you can set the belt or dial on a drill press. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Answer first. The speed you want is the cutting speed for the material divided by the bit circumference: RPM = SFM x 12 / (pi x diameter in inches). Bigger bits need fewer RPM, softer materials allow more.
Worked example
Drilling aluminium with a 1/2 in bit: 3056 to 7639 RPM. The maths is RPM = SFM x 12 / (pi x diameter), so 400 SFM gives 400 x 12 / (3.1416 x 0.5) = 3056 RPM and 1,000 SFM gives 7639 RPM. In practice you start near the low end and speed up only if the chips and finish are good.
How it works
Formula. RPM = cutting speed (SFM) x 12 / (pi x diameter in inches). In metric, RPM = cutting speed (m/min) x 1000 / (pi x diameter in mm). The result is a range because the published cutting speed for each material is a range.
What the figures are. The surface speeds come from the Wikipedia speeds-and-feeds table for a plain high-speed-steel cutter at a 1 hour tool life, dry cutting and medium feeds. That is a starting point, not a guarantee: coolant, cobalt or carbide tools, rigidity and the exact alloy all move the best speed. When unsure, the lower half of the range is the cautious choice.
Materials left out. Stainless steel, cast iron, bronze and a few others are not listed because the source table gives figures that do not agree between its feet-per-minute and metres-per-minute columns, and this tool only uses numbers that check out. For those, use your tool maker's data sheet.
Wood. The source says drilling wood generally uses higher spindle speeds than metal and that larger bits need slower speeds to avoid burning. Wood is far less critical than metal.
Safety. Wear eye protection, clamp the work (never hold small pieces by hand) and keep loose sleeves, hair and gloves away from the spindle. Do not exceed the maximum speed marked on the bit or the machine. These are general starting figures, not professional machining advice.
Sources
- Speeds and feeds - Wikipedia (opened 2026-10-08)
The cutting-speed ranges and the RPM formula are from the page above. Conversions use 1 ft = 0.3048 m and 1 in = 25.4 mm.
FAQ
What RPM should I drill steel at?
For mild steel the source gives a wide 10 to 125 surface feet per minute for a plain high-speed-steel cutter. A 1/4 in bit at 10 SFM is about 153 RPM and at 125 SFM about 1,910 RPM. Start low, use cutting fluid, and watch the chips.
Why does a bigger drill bit need a lower RPM?
The edge of a bigger bit travels farther each turn, so for the same surface speed the spindle must turn slower. Doubling the diameter halves the RPM.
Is this the same as the SFM calculator?
No. This tool starts from the material and gives RPM. The surface speed calculator does the reverse: you enter RPM and diameter and it reports SFM.
Why is stainless steel not listed?
The only table we could verify listed figures for stainless that disagreed between its two unit columns, so it was left out rather than guessed. Check your tool supplier for stainless.
Do these speeds work for carbide or cobalt bits?
They are for a plain high-speed-steel cutter. Cobalt and carbide tools generally tolerate higher speeds, but this page does not publish those numbers, so follow the maker's data.