CNC Feed Rate Calculator
Spindle speed from the cutting speed and tool diameter (rpm = Vc × 1000 ÷ π D, or SFM × 12 ÷ π D), feed rate from chip load, flutes and rpm, and the material removal rate from the width and depth of cut, in metric or inch units.
Result…
How it's calculated
rpm = Vc (m/min) × 1000 ÷ (π × D mm) rpm = SFM × 12 ÷ (π × D in) Feed rate = rpm × chip load × flutes MRR = ae × ap × feed rate (÷ 1000 for cm³/min)
The spindle speed that gives a cutting speed Vc at the edge of a tool of diameter D is Vc ÷ (π D), with 1000 turning metres into millimetres or 12 turning feet into inches. The feed rate (table feed) is the distance the tool travels per minute: the chip load each flute takes, times the flutes, times the rpm. The material removal rate multiplies the width of cut, the depth of cut and the feed rate. These are the standard machining relations given by Sandvik Coromant and in the Wikipedia article on speeds and feeds. Cutting speed and chip load depend on the tool, coating, material and setup, so take them from the tool maker. 1 in = 25.4 mm exactly.
Your numbers, step by step
About the CNC Feed Rate calculator
This CNC feed rate calculator turns the cutting speed and chip load your tool maker publishes into numbers you can type into a program: the spindle speed in rpm, the feed rate in mm/min or in/min, the feed per revolution and the material removal rate. It works in metric (millimetres and metres per minute) or inch units (inches and surface feet per minute), and you can start from a cutting speed or from an rpm you already know, such as your spindle's top speed. Add the width and depth of cut to see how much material each minute removes, and a length of cut to time one pass. Every step shows your own numbers, so you can check the arithmetic against a tool catalogue. It does not invent cutting data: the right values depend on the tool, coating, material and machine.
How to use it
- Pick the “Units” and choose whether the “Spindle speed from” is a “Cutting speed” or “I know the rpm”.
- Enter the “Tool diameter” and the “Cutting speed” from the tool maker's data, or your “Spindle speed”.
- Enter the “Chip load (feed per tooth)” and the “Number of flutes”.
- Add the “Width of cut (radial, ae)” and “Depth of cut (axial, ap)” for the removal rate, or enter 0 to skip it.
- Read the feed rate, the spindle speed and the removal rate, and check the rpm against your machine's limit.
Worked example
A 10 mm three-flute end mill at a cutting speed of 120 m/min: rpm = 120 × 1000 ÷ (π × 10) = 3,820 rpm. With a chip load of 0.05 mm per tooth, the feed per revolution is 0.05 × 3 = 0.15 mm and the feed rate is 3,820 × 0.15 = 573 mm/min (22.56 in/min). Cutting 5 mm wide and 10 mm deep removes 5 × 10 × 573 ÷ 1000 = 28.6 cm³ per minute.
Updated
Questions people ask
How do I calculate spindle speed from cutting speed?
Metric: rpm = cutting speed in m/min × 1000 ÷ (π × diameter in mm). Inch: rpm = SFM × 12 ÷ (π × diameter in inches). Both are the relations given in the Wikipedia article on speeds and feeds.
What is the formula for CNC feed rate?
Feed rate = rpm × chip load × number of flutes. A 2-flute cutter at 10,000 rpm and 0.03 mm per tooth feeds at 600 mm/min.
Where do I find the right chip load and cutting speed?
From the tool maker's catalogue or website for that exact tool, coating and workpiece material. Start at the lower end for long-reach tools, slotting or a light machine, then adjust from the chips and the sound of the cut.
Why is my feed rate too slow when I use a narrow width of cut?
At a width of cut well under half the diameter the chip gets thinner than the chip load you set, an effect called chip thinning. Tool makers publish corrections for it; this calculator uses the plain chip load you enter.
How is material removal rate worked out?
Multiply the width of cut by the depth of cut and the feed rate. In millimetres the result is mm³/min, so divide by 1000 for cm³/min; in inches it is already in³/min. Check the spin of the cutter itself with the angular velocity calculator.
What can this feeds and speeds calculator not tell me?
It does not know your machine's power, rigidity or the tool's stick-out, and it does not check spindle torque at low rpm. Treat the result as a starting point and follow the tool maker's limits.