How to use the cutting speed and rpm calculator
See in one screen how many revolutions per minute a cutting speed asks for at a given tool diameter, and what cutting speed the rpm you are running actually gives. Diameter and cutting speed alone give the rpm, diameter and rpm alone give the cutting speed, and with all three fields filled both directions appear together, so the number on the machine and the figure in the tooling data can be compared side by side.
The relation applied is geometric: rpm = 12 x SFM / (pi x D), about 3.82 x SFM / D, and SFM = pi x D x rpm / 12, with the diameter in inches and the cutting speed in surface feet per minute. The 12 converts inches of circumference into feet, and it is the same relation as the metric N = 1,000 x Vc / (pi x D) with D in millimeters and Vc in meters per minute, so the cutting speed result also shows m/min in parentheses. For example, a 0.5 in end mill at 400 SFM needs about 3,056 rpm. The two lines are the same relation read in opposite directions, so a gap between them means the rpm and the cutting speed you entered describe different conditions. As of October 2026.
Cutting speeds by material, tool life limits and suggested cutting conditions were not confirmed in an authoritative source, so none are given here. Enter the values from the tool maker data sheet. Feed rate, feed per tooth and feed per revolution are not covered, and cutting force and spindle power are not calculated. This calculator is for reference and does not replace design; confirm final cutting conditions against the tooling data and the machine rating.
Frequently asked questions
Cutting speeds by workpiece material were not confirmed in an authoritative source, so this page suggests none. Enter the value from the tooling maker data you are working with.
The diameter of the rotating part. For milling and drilling that is the tool diameter; on a lathe it is the diameter being cut on the workpiece.
Feed rate and feed per tooth are not covered. This page only converts between cutting speed and spindle speed in both directions.