ONLINE TURNING CALCULATOR / RPM
CNC lathe RPM calculator
Convert cutting speed and the diameter at the calculation point to theoretical spindle RPM. Optionally compare it with a maximum RPM value you have already confirmed from machine documentation.
Formula and limits
Metric: n = 1000 × Vc ÷ (π × D), where Vc is m/min and D is mm. Imperial: n = 12 × SFM ÷ (π × D), where D is inches. The formula is referenced in NTK Cutting Tools’ turning calculation material.
This is a theoretical conversion. Choose actual cutting speed using material, insert grade, depth of cut, coolant, machine rigidity, and process requirements. In constant-surface-speed mode, RPM rises as diameter decreases. This page does not set or verify a controller speed limit; the optional comparison is arithmetic only.
G96/G97 meanings, units, and speed-limit codes depend on the control. No CNC program is generated here. See the controller differences and review guide.
Sources: NTK Cutting Tools — Calculation Formula for Turning (formula reference, not cutting advice); Haas NGC Lathe Operator’s Manual (2024) (Haas control context only).