CNC Speeds and Feeds Calculator
Spindle speed (RPM) = (Vc × 1000) ÷ (π × D). Feed rate (mm/min) = RPM × fz × number of flutes.
Spindle speed
— RPM
Feed rate
— mm/min
Engineering estimate — verify before machining.
How it works
Enter tool diameter D, flute count Z, cutting speed Vc and feed per tooth fz. Spindle speed is the speed that gives the requested surface speed at the tool diameter; feed rate is spindle speed multiplied by feed per tooth and the number of flutes. If you enter a machine maximum RPM, the spindle speed is capped and the feed rate recalculated from the capped value.
Imperial units
RPM = (SFM × 12) ÷ (π × D in inches). Feed (in/min) = RPM × IPT × Z.
Limitations
This is an estimate. It does not account for machine rigidity, tool overhang, coolant, engagement or workpiece batch variation. Use cutting speed and feed values from approved tool data, and verify before machining.
FAQ
What is chip load?
Chip load, or feed per tooth (fz), is the thickness of material each cutting edge removes per revolution.
How do I calculate spindle speed?
RPM = (cutting speed × 1000) ÷ (π × tool diameter in mm).
How do I calculate feed rate?
Feed rate = RPM × feed per tooth × number of flutes.
Are these values safe to use directly?
No. They are starting estimates. Verify against tool manufacturer data and your machine capability before machining.