NTB SpecPro

Cutting speed and RPM calculator

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Free tool · Machining

Cutting speed and spindle speed (RPM) calculator

Enter the diameter and cutting speed (Vc) to get the spindle speed (n) instantly, or enter the RPM to find the cutting speed. Use the machined workpiece diameter for turning and the tool diameter for milling and drilling. Everything runs in your browser; no data is sent.

Also available in: Türkçe · العربية

Spindle speed n (rev/min)–
Cutting speed Vc (m/min)–
Cutting speed (SFM, ft/min)–

n = Vc · 1000 / (π · D) · Vc = π · D · n / 1000 · Vc (m/min), D (mm), n (rev/min) · 1 m/min = 3.281 ft/min · Example: D = 50 mm, Vc = 200 m/min → n ≈ 1273 rev/min

Cutting speed is the speed at the cutting edge; for the same cutting speed, a smaller diameter means higher RPM. When facing on a lathe the diameter changes continuously, so the machine runs either at constant cutting speed (RPM changes) or at constant RPM (cutting speed changes). Take the starting cutting speed from the tool manufacturer's catalogue for your material and insert grade.

From drawing to inspection report: the Quality control moduleBallooning, measurement records, Cp/Cpk tracking and the AS9102 first article report under one part number.
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Frequently asked

Which diameter is used for turning?The diameter being machined, i.e. the diameter the cutting edge is touching at that moment. In roughing with a large difference between the raw and finished diameter, calculate for both diameters.
Which diameter is used for milling and drilling?The tool diameter: the cutter diameter for end mills, the drill diameter for drills. With a ball-nose cutter at a small axial depth, the effective diameter in contact is smaller than the tool diameter, so the RPM rises.
Where do I find the cutting speed?The tool manufacturer's catalogue gives a starting range for the workpiece material and insert grade. Adjust it by trial for fixture rigidity, coolant and target tool life.
Is there a link between RPM and parts drifting out of tolerance?There can be. Too high a cutting speed accelerates tool wear, and a worn tool slowly shifts the diameter in series production. To follow the drift, enter the measurements in time order into the Cp/Cpk tool.