Maker and DIY Calculators
CNC feeds and speeds.
Your cutter maker gives a surface speed and a chip load for your material. This calculator turns them into spindle RPM and feed rate for your cutter size and flute count, and shows what happens if your spindle cannot reach that RPM.
RPM = surface speed / (pi x diameter). Feed rate = RPM x flutes x chip load. 6 mm cutter, 2 flutes, 120 m/min surface speed and 0.03 mm chip load: 6,366 RPM and 382 mm/min.
Cutter and recommendations
Speeds and feeds
Fill the form and press Calculate.
Worked example
A 6 mm two-flute end mill with a recommended surface speed of 120 m/min and a chip load of 0.03 mm per tooth. RPM = 120 x 1,000 / (pi x 6) = 6,366 RPM. Feed rate = 6,366 x 2 x 0.03 = 382 mm/min. The same job in imperial: 0.25 in cutter at 400 SFM gives 400 x 12 / (pi x 0.25) = 6,112 RPM. The values are illustrative; use your own maker's figures.
How it works
Surface speed is how fast the cutting edge moves past the material, so spindle RPM follows from the circumference of the cutter: RPM = surface speed / (pi x diameter). Feed rate is how far the tool advances per minute: RPM x number of flutes x chip load, where chip load is the feed per tooth.
Imperial inputs are converted with 0.3048 m per foot and 25.4 mm per inch. If you enter a spindle RPM limit and the ideal RPM is higher, the tool uses the limit and computes the feed from that RPM, which holds chip load constant but lowers surface speed.
Not included. Material tables, chip thinning at light stepover, depth and stepover limits, deflection, spindle power and tool life. Wear eye protection and secure the work.
Sources (opened 2026-10-08). Speeds and feeds - Wikipedia for the spindle speed formula (surface speed divided by pi times diameter, with its metric and imperial forms) and the feed rate formula FR = RPM x T x CL (teeth and chip load). This page supplies no surface speed or chip load values: those come from your cutter maker, and the example numbers are placeholders.
FAQ
How do I calculate RPM for a CNC router or mill?
Divide the recommended surface speed by pi times the cutter diameter, keeping units consistent: RPM = m/min x 1000 / (pi x mm), or SFM x 12 / (pi x inches).
How do I calculate feed rate?
Multiply spindle RPM by the number of flutes and the chip load per tooth. The result is in mm per minute or inches per minute depending on your chip load units.
Where do I get surface speed and chip load?
From your cutter maker's data for your material and cutter. This calculator does not supply material values, and the defaults are placeholders.
What if my spindle cannot reach the RPM?
Enter the maximum RPM. The calculator uses it and sets the feed from that RPM, so chip load stays as entered, but surface speed drops. Check the cutter maker's guidance for slow spindles.
Are these values safe to run as is?
Treat them as a starting point. Rigidity, work holding, depth of cut and the machine all matter, so test on scrap and adjust. Wear eye protection.
Disclaimer
Estimates from the numbers you enter. Machining can cause serious injury; use proper guarding, eye protection and work holding. Cutting parameters here are starting points, not machine-specific advice.