Cutting speed to RPM converter
Convert a recommended surface speed to spindle speed for your drill, end mill or workpiece diameter, or RPM back to SFM and m/min.
That's 1.83× as fast as carbide in titanium, while carbide in stainless steel is 1.09× faster.
What it means
How fast is that cut?
Pick the diameter of the rotating part: the tool on a mill or drill, the workpiece on a lathe. Speeds for materials are starting points; follow the tool maker’s data.
Every unit
That speed in every unit
Learn
Three things worth knowing
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SFM × 3.82 ÷ inches
rpm ≈ 3.82 × SFM ÷ diameter in inches, or 318 × m/min ÷ diameter in mm.
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Taylor’s experiments
Frederick Taylor spent 26 years and 800 tons of steel testing cutting speeds; his 1907 tool-life equation still sets the numbers in catalogs.
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Same rpm, every tool
Running a big cutter at a small drill’s rpm burns it out: the edge moves several times too fast.
Shortcuts
Popular cutting speed conversions
Background
About cutting speed
Tool makers give a cutting speed: how fast the edge moves through the material, in surface feet per minute (SFM) or meters per minute. The machine is set in rpm, and the link is the circumference: rpm = speed ÷ (π × diameter).
A small drill needs a high rpm to reach the same surface speed as a big one: 100 m/min is 3,180 rpm on a 10 mm cutter but 637 rpm on a 50 mm one.