Torque & Horsepower Calculator - Engine RPM, lb-ft & Kilowatts

Calculate mechanical horsepower from torque (lb-ft or N·m) and engine RPM, or calculate required motor torque and metric kilowatts (kW).

⚙️ Configuration & Inputs

Engine / Motor Torque Rotational force applied at shaft

Torque Unit

Rotational Speed (RPM) Revolutions per minute (5252 RPM crossover)

📊 Results & Analysis

Mechanical Horsepower 350.0 HP 261.0 Kilowatts (kW)

Torque in lb-ft 350.0 lb-ft 474.5 N·m (Metric)

Metric Horsepower (PS / CV) 354.9 PS Pferdestärke (European rating)

Rotational Work Done 260,996 Watts Joules per second

Torque vs Horsepower: The 5,252 RPM Relationship

Torque is the rotational twisting force an engine produces, while horsepower is the rate at which that work is done over time.

1. The Golden 5,252 Equation

Horsepower = (Torque in lb-ft × RPM) / 5252

Because of the mathematical derivation from 33,000 ft-lbs/minute and 2π radians per revolution: 33,000 / (2π) ≈ 5252.113. On any dyno graph plotted with equal scaling, torque (in lb-ft) and horsepower will always cross and equal each other at exactly 5,252 RPM!

2. Metric Torque Conversion

For international specifications in Newton-meters (N·m) and Kilowatts (kW):

Power (kW) = (Torque in N·m × RPM) / 9549

Frequently Asked Questions

In imperial units, horsepower is defined as 550 ft-lbs/sec (or 33,000 ft-lbs/min). One revolution represents 2π radians. Dividing 33,000 by 2π yields 5252.11. At 5,252 RPM, the RPM and 5,252 cancel each other out, making HP exactly equal to torque.

In strict engineering nomenclature, pound-feet (lb-ft) refers to torque (rotational moment), while foot-pounds (ft-lb) refers to energy or work done. However, automotive publications frequently use them interchangeably.

Yes. High low-end torque provides immediate pulling force at low engine speeds (1500 - 2500 RPM) needed to move heavy trailers from a dead stop, whereas horsepower allows high-speed cruising and acceleration at higher RPMs.