Turning Speeds and Feeds Calculator: RPM & Feed

Published September 22, 2026 · MfgWorkbench editorial reference

Convert turning cutting speed and feed per revolution into spindle RPM and linear feed. Enter the actual cutting diameter and an RPM limit appropriate to the approved setup.

Turning formulas and unit choices

For metric inputs, n = 1000 Vc/(πD), where Vc is m/min and D is mm. For inch inputs, n = 12 V/(πD), where V is ft/min and D is inches. Linear feed is n × f, with f in mm/rev or in/rev. Unlike a milling chip-load calculation, do not multiply turning feed by a flute count.

The tool reports both calculated RPM and RPM limited by your entered cap. The corresponding feed and actual surface speed use the capped RPM. Switching the unit selector changes how values are interpreted; it does not automatically convert values already entered.

Example: 50 mm stock at 150 m/min

Calculated speed is 954.930 RPM. At 0.20 mm/rev, linear feed is 190.986 mm/min. If the approved setup is limited to 800 RPM, feed becomes 160 mm/min and actual cutting speed is 125.664 m/min. This separates a target cutting speed from a machine or workholding constraint.

Diameter changes and production limits

A smaller diameter needs more RPM to maintain the same cutting speed. During facing, the diameter approaches zero; unlimited constant-surface-speed calculations therefore become inappropriate. Program and prove the spindle-speed cap required by the machine and workholding documentation.

Material grade, insert geometry, coating, nose radius, interruption, overhang and coolant affect a suitable cutting speed or feed. Obtain those inputs from the tooling supplier. The default values demonstrate the arithmetic, not recommended settings for an unnamed material. Check chuck rating, gripping force, stock projection, torque and vibration before using any calculated value.