CNC Speed (RPM) Calculator
Calculate the spindle speed (RPM) for a CNC operation from cutting speed and tool diameter.
How it works
- 1Enter the recommended cutting speed (Vc) from your tool or material data in m/min or ft/min.
- 2Enter the tool or workpiece diameter in mm or inches.
- 3The calculator applies N = 1000·Vc / (π·D) and returns the spindle RPM to program.
Use cases
- Setting spindle speed for end mills, drills, and turning inserts.
- Converting a recommended surface speed into RPM for a new material or tool.
- Checking a programmed RPM matches the target cutting speed before a job.
Frequently asked questions
What is the spindle speed formula?
N (rpm) = 1000·Vc / (π·D), with Vc in m/min and D in mm. A 50 mm tool at 150 m/min gives N ≈ 955 rpm.
Where do I find the recommended cutting speed?
Tool maker catalogues list Vc ranges per tool–material pair. Starting points: aluminium 200–400 m/min (carbide), mild steel 80–200, stainless 50–120.
Does this work for milling and turning?
Yes. In turning, D is the workpiece diameter; in milling, the cutter diameter. The formula is identical.
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