CNC Feed Rate & Speed Calculator
Turn spindle RPM, flute count and chip load into a CNC feed rate, and get the cutter surface speed for milling and routing.
How it works
Feed rate = RPM × flutes × chip load · Surface speed = π × diameter × RPM ÷ 1000
Feed rate is the product of how fast the spindle turns, how many cutting edges pass per turn, and how thick a chip each edge should take — the chip load. Chip load is the number that actually protects the tool: too low and the edge rubs and overheats, too high and it snaps, so the tool maker publishes a range for each material and diameter. Surface speed (the rim velocity of the cutter) is the other half of the picture and is what you match to the material when picking the RPM in the first place.
Worked example
A 2-flute 6 mm end mill at 18,000 RPM with a 0.05 mm chip load feeds at 18,000 × 2 × 0.05 = 1,800 mm/min. Its surface speed is π × 6 × 18,000 ÷ 1000 ≈ 339 m/min.
Frequently asked questions
What is chip load and why does it matter?
Chip load is the thickness of material each cutting edge removes per pass. It is the key to tool life: below the recommended range the tool rubs instead of cutting and overheats, above it the flute is overloaded and can chip or break.
Should I set RPM or feed rate first?
Set RPM from the recommended surface speed for the material and cutter diameter, then calculate the feed rate from that RPM, the flute count and the chip load. The feed follows the speed, not the other way around.
Does this work for routers and lathes too?
The feed-rate formula applies to any rotating multi-flute cutter, including CNC routers. On a lathe the workpiece spins instead of the tool, so surface speed is based on the workpiece diameter, but the same relationship holds.
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This calculator is for educational purposes. Double-check important results before acting on them.