BLDC / PMSM Speed Calculator
Electrical frequency, electrical RPM and commutation rate from pole pairs and mechanical speed.
Input
ℹ Pole pairs = poles ÷ 2. Electrical speed = mechanical × pole pairs.
Results
Electrical Speed—
Electrical Frequency—
Commutations—
💡 Usage & Formula
f_elec (Hz) = RPM × pole pairs / 60; electrical RPM = RPM × pole pairs. 6-step commutation = pole pairs × 6 per mechanical rev.
When you need it: Relating electrical drive frequency, pole count and mechanical RPM for a brushless motor, and using Kv to predict no-load speed from supply voltage.
Worked example: RPM = 120 × f / poles, so an 8-pole motor at 100 Hz electrical spins 120 × 100 / 8 = 1500 RPM. No-load speed ≈ Kv × Vsupply.
Tips & gotchas:
- Mechanical RPM equals the electrical frequency divided by the number of pole pairs, not poles.
- Kv and the torque constant are inverses — a high-Kv motor spins fast but makes less torque per amp.
- Field weakening pushes speed above the base value at the cost of available torque.
- Commutation needs rotor position from Hall sensors, an encoder, or a sensorless back-EMF estimator.
📖 References:BLDC motor (Wikipedia)