How to use this calculator
Enter the motor's rated power (in kilowatts or horsepower), its rated speed in RPM, and the load factor — the percent of rated power it's actually delivering. Click Calculate to get the full-load torque, the torque at your specified load, and the shaft's angular velocity. Click Reset to restore the default example values.
The formula
Torque, power, and rotational speed are related by T = P / ω, where ω (omega) is the angular velocity in radians per second. Since ω = 2πN/60 for a speed N in RPM, this simplifies to the standard motor-sizing shortcuts:
- Metric: T (N·m) = 9549 × P (kW) / N (RPM)
- Imperial: T (lb-ft) = 5252 × P (hp) / N (RPM)
Both forms come from the same physics: mechanical power equals torque times angular velocity. The rated (nameplate) power of a motor is its output shaft power, so no efficiency adjustment is needed to get full-load torque — efficiency only matters when converting electrical input power to mechanical output power, which is a separate calculation.
Understanding the inputs
Motor Power Rating and Power Unit describe the nameplate rating (for example, 5 kW or 7.5 hp). Motor Speed (RPM) is the rated full-load speed shown on the nameplate — not the no-load synchronous speed, which is always somewhat higher due to slip in AC induction motors. Load Factor lets you scale the result to a partial load: since torque is proportional to power at constant speed, running at 75% of rated power delivers 75% of rated torque (at the same speed).
Interpreting the results
Full-Load Torque is the torque available when the motor is delivering its full rated power at its rated speed, shown in both N·m and lb-ft. Torque at Load Factor scales that figure by the load percentage you entered. Angular Velocity converts the rated RPM into radians per second, the unit the underlying physics equation uses directly.
Frequently Asked Questions
What is the formula for electric motor torque?
Why does higher RPM mean lower torque for the same power?
Should I use rated (nameplate) power or electrical input power?
What is the difference between full-load torque and starting torque?
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |