Speeds and Feeds Calculator
Enter the cutting speed, tool diameter, chip load, and number of flutes to find spindle RPM and feed rate.
How speeds and feeds are calculated
Spindle speed is found from RPM = (SFM × 12) / (π × diameter), converting the material's recommended surface cutting speed into a rotational speed based on the tool's diameter — a larger tool reaches the same surface speed at a lower RPM.
Feed rate (how fast the tool moves through the material) is RPM × chip load per tooth × number of flutes — each flute removes one chip load's worth of material per revolution, so more flutes or a higher chip load allow a faster feed at the same RPM.
Frequently asked questions
What is SFM and where do I find a value for my material?
SFM (surface feet per minute) is the recommended cutting speed for a given material and tool combination, found in machining handbooks or tool manufacturer charts. Harder materials generally need lower SFM; softer materials can run faster.
What is chip load and why does it matter?
Chip load is the thickness of material each tooth removes per revolution. Too low a chip load can cause rubbing and excess heat; too high can break the tool or produce a poor finish — manufacturers publish recommended chip load ranges per tool and material.
Why does a bigger tool need a lower RPM for the same cutting speed?
Surface speed is the rate at which the edge of the tool moves through the material, which depends on both RPM and the tool's circumference. A larger diameter tool covers more distance per rotation, so it needs fewer rotations per minute to achieve the same surface speed.