CNC Machining calculator
Material Removal Rate Calculator
Size a roughing pass before you run it: removal rate sets cutting time, and spindle power decides whether the machine can pull it. You need stepover, depth, feed, the material's unit power and your spindle's power.
What this calculator does
- Material removal rate of a milling pass, and the spindle horsepower it needs against the power you have.
Formula used
- Material removal rate = radial depth of cut × axial depth of cut × feed rate
- Power at the cutter = removal rate × unit power
- Spindle power needed = power at the cutter ÷ (drive efficiency ÷ 100)
- Spindle load = needed ÷ available spindle power × 100; power headroom = available − needed
- Removal rate at full power = available spindle power × drive efficiency ÷ 100 ÷ unit power
Inputs explained
- Radial Depth of Cut: Stepover from the CAM toolpath, measured across the cutter.
- Axial Depth of Cut: Depth of each pass along the tool axis.
- Feed Rate: Programmed cutting feed, not rapids or an average.
- Unit Power: Handbook value for the material; about 0.3 aluminum, 1.0 stainless.
- Spindle Drive Efficiency: Share of motor power that reaches the cutter, from the machine manual.
- Available Spindle Power: Power-curve value at your RPM, less any reserve you keep.
How to use the result
- Best suited to checking a roughing pass against spindle horsepower, comparing a full slot with a side cut.
- Handbook unit powers assume a 0.010 in chip; thinner chips take more power per in³. Checks power only, not spindle torque at low RPM, deflection, chatter or chip evacuation.
Current U.S. benchmarks
- The producer price index for steel mill products stands at 381.162 (BLS, Aug 2026), up 23.4% from a year earlier. Quotes priced off last quarter's material cost miss this move.
- The U.S. has 17,154 machine shops establishments employing about 223,303 workers (Census County Business Patterns, 2023).
Common questions
- What unit power should I use for my material? Use a handbook table for your material and hardness. Michigan State's machining notes list 0.3 hp per in³/min for aluminum alloys, 0.6 to 1.0 for carbon steel and 1.0 for stainless. Divide a metric Kc in N/mm² by 2,730 to convert.
- Why does the spindle need more power than the cut? Belts, gears and the motor lose part of the power before it reaches the tool. Drive efficiency covers that loss; Mitsubishi Materials' worked examples use 80%, so enter your machine's own figure if the manual gives one.
- Is the nameplate spindle rating the power I have? Only where the power curve reaches that rating. Spindle power varies with speed, so read the curve at your programmed RPM and enter that value, less any reserve you want to keep.
- How do I turn removal rate into cutting time? Divide the stock volume in cubic inches by the removal rate. A 12 in³ pocket at 12 in³/min is one minute of cutting, before rapids, tool changes and finishing passes.
Related guides
Last reviewed 2026-10-01.