Workshop and Metalwork Calculators
Surface speed.
Enter the spindle speed and the diameter of the cutter or the part. You get the surface speed in feet per minute and metres per minute, and a quick check against common material ranges. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Answer first. Surface speed is how fast the edge of the tool passes the work: SFM = pi x diameter (in) x RPM / 12. Metric: m/min = pi x diameter (mm) x RPM / 1000.
Worked example
A 1/2 in cutter at 3,000 RPM: SFM = pi x 0.5 x 3000 / 12 = 392.7 SFM, which is 119.7 m/min. Against the table that is below the aluminium range of 400 to 1,000 SFM and above the mild steel range of 10 to 125 SFM.
How it works
Formula. SFM = pi x D x RPM / 12 with D in inches, or m/min = pi x D x RPM / 1000 with D in millimetres. The same number applies to a drill, an end mill, a saw blade or a part turning in a lathe.
Comparison column. The ranges come from the Wikipedia speeds-and-feeds table for a plain high-speed-steel cutter, 1 hour tool life, dry cutting, medium feeds. "Within" means your figure falls inside the published range; it does not mean the cut is ideal. Rows whose two unit columns disagreed in the source are not used.
Lathe note. On a lathe, the surface speed falls as the tool moves toward the centre because the diameter shrinks, so the RPM would have to rise to hold it constant.
Safety. Never run a tool, blade or grinding wheel faster than its marked maximum speed; overspeeding a grinding wheel in particular can destroy it. Wear eye protection and guard moving parts. These are general figures, not professional machining advice.
Sources
- Speeds and feeds - Wikipedia (opened 2026-10-08)
The formula and the material ranges are from the page above. Unit conversions use 1 ft = 0.3048 m and 1 in = 25.4 mm.
FAQ
What does SFM mean?
SFM is surface feet per minute: the distance the cutting edge travels past the material each minute, in feet. The metric version is metres per minute.
How do I convert SFM to RPM?
Rearrange the formula: RPM = SFM x 12 / (pi x diameter in inches). The drill speed calculator does this for a chosen material.
How do I convert m/min to SFM?
Divide by 0.3048 (one foot in metres). For example 100 m/min is about 328 SFM.
Does the diameter mean the cutter or the workpiece?
Whichever is turning. A drill or end mill uses the tool diameter; turning on a lathe uses the diameter of the part at the cut.
Is a result inside the range always safe?
No. The ranges are starting points for a plain high-speed-steel tool. Rigidity, coolant, tool coating and the alloy all change what works.