kW · hp · N·m
Machining Power & Torque Calculator
Estimate spindle and motor power from metal removal rate using the unit power method, and convert between power and torque at any RPM. Includes a material unit-power reference table.
Power from metal removal rate
P = Q × unit powerTorque from power & RPM
T = 9550 × kW / nPower from torque & RPM
P = T × n / 9550Unit power reference table
Unit power is the spindle horsepower needed to remove one cubic inch per minute (or kW per cm³/min). Values assume sharp tools; add 25–50% for worn tools.
| Material | Unit power (hp per in³/min) | kW per cm³/min |
|---|---|---|
| Mild steel 85–95 HRB | 1.0 | 0.0455 |
| Steel 25–35 HRC | 1.4 | 0.0637 |
| Steel 35–45 HRC | 1.6 | 0.0728 |
| Stainless steel | 1.3 | 0.0592 |
| Cast iron | 0.7 | 0.0319 |
| Aluminum alloys | 0.33 | 0.0150 |
| Brass / bronze | 0.5 | 0.0228 |
| Copper | 0.7 | 0.0319 |
| Titanium alloys | 1.2 | 0.0546 |
| Nickel superalloys (Inconel) | 2.0 | 0.0910 |
| Hardened steel 45–55 HRC | 2.1 | 0.0956 |
Formulas used
Unit power: P_spindle = Q (in³/min) × p; P_motor = P_spindle ÷ machine efficiency
Torque: T (N·m) = 9550 × P (kW) / n (RPM) · T (ft·lb) = 5252 × P (hp) / n
Note: available torque rises as RPM falls — check the torque curve, not just the power rating, for large-diameter low-speed tools.
Frequently asked questions
How much horsepower does machining steel take?
Roughly 1 hp per cubic inch per minute for mild steel (about 0.046 kW per cm³/min), 1.3–1.6 for harder steels and stainless, 0.33 for aluminum and about 2 for nickel superalloys — at the spindle, before efficiency losses.
How do I get spindle torque from kW and RPM?
T (N·m) = 9550 × P (kW) / n (RPM). An 11 kW spindle at 1500 RPM delivers about 70 N·m; the same spindle at 300 RPM delivers about 350 N·m — if the drive allows constant power down that far.