Estimate motor power in kW from operating frequency, rated power, and rated Hz for pump, fan, or conveyor loads with torque scaling.

Estimates motor output power when a VFD runs the motor below or above its rated frequency.

Pump and fan power scales with the cube of speed; constant-torque loads scale linearly.

Results are estimates. Field weakening above rated frequency, slip, and motor losses can reduce real-world output.

Hz To Kw Formula

The following formula estimates mechanical shaft power (kW) from electrical frequency (Hz), pole count, and shaft torque for a synchronous motor/generator operating at synchronous speed (i.e., neglecting slip and losses).

P₍kW) = (4π f) / (P_c × 1000)

Variables:

  • P is the power output (kW)
  • τ is the shaft torque (N·m)
  • f is the frequency (Hz)
  • P_c is the pole count
Hz to kW Example Table (Assumes synchronous speed, Pc = 4 poles, τ = 10 N·m)
Frequency (Hz) Power (kW)
50.157
100.314
150.471
200.628
300.942
401.257
501.571
601.885
752.356
902.827
1003.142
1203.770
1504.712
1805.655
2006.283
2407.540
3009.425
36011.310
40012.566
50015.708
* Rounded to 3 decimals. Formula: P(kW) = (4π f τ) / (Pc × 1000). Assumes torque τ = 10 N·m and pole count Pc = 4. 1 kW = 1000 W.

What is Hz To Kw?

Hz (hertz) is a unit of frequency (cycles per second), while kW (kilowatt) is a unit of power. There is no universal “Hz to kW” conversion because power depends on the system. In rotating AC machines, frequency and pole count determine synchronous speed (for example, 60 Hz and 4 poles corresponds to 1800 rpm), and with a known shaft torque you can estimate mechanical power using P = τ·ω. (If you need electrical real power from voltage/current, frequency is not a multiplicative factor; for example, three‑phase real power is P(kW) = √3 · V · I · PF / 1000.)

How to Calculate Hz To Kw?

The following steps outline how to estimate mechanical kW from frequency using the given formula:

  1. Determine the frequency (f) in hertz (Hz).
  2. Determine the pole count (Pc) of the machine (2, 4, 6, …).
  3. Determine the shaft torque (τ) in newton‑meters (N·m).
  4. Calculate the synchronous angular speed: ω = 4πf / Pc (rad/s).
  5. Calculate mechanical power in watts: P(W) = τ · ω.
  6. Convert watts to kilowatts: P(kW) = P(W) / 1000, which gives P(kW) = (4π f τ) / (Pc × 1000).

Example Problem:

Use the following variables as an example problem to test your knowledge:

frequency (f) = 60 Hz

pole count (Pc) = 4

shaft torque (τ) = 10 N·m

power (P) = (4π · 60 · 10) / (4 · 1000) = 1.88496 kW