Work out cutting speed instantly with clear inputs, formula shown and shareable results.
Cutting speed is the surface velocity where the tool meets the work: pi times diameter times rpm, divided by 12 to give feet per minute. Every tool material has a recommended range, so knowing the speed a given diameter and rpm produces is what lets a handbook figure be applied to the machine in front of you.
Cutting speed
SFM = pi x D in x rpm / 12
Inverse
rpm = 12 x SFM / (pi x D)
SFM = pi x D in x rpm / 12. Cutting speed is the surface velocity where the tool meets the work: pi times diameter times rpm, divided by 12 to give feet per minute.
Surface speed depends on diameter. A 1/8 inch drill at 800 rpm cuts at only 26 SFM, far below the recommended range, so small tools must spin much faster to reach the same cutting speed.
This calculator takes 2 inputs: Tool or workpiece diameter, Spindle speed. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.