Engine Horsepower Calculator

Horsepower and torque are two related but distinct measures of an engine’s performance. Torque is the rotational force the engine produces; horsepower is how fast that force can be delivered. They are mathematically linked through engine speed (RPM).

Core conversion formula: Horsepower = (Torque × RPM) ÷ 5,252

Solving for torque: Torque = (Horsepower × 5,252) ÷ RPM

Solving for RPM at peak power: RPM = (Horsepower × 5,252) ÷ Torque

Where does 5,252 come from? It is derived from the definition of horsepower: 1 HP = 33,000 ft-lbs per minute One revolution = 2π radians 5,252 = 33,000 ÷ (2π) — the unit conversion constant connecting HP, torque, and RPM.

What each variable means:

• Torque (ft-lbs or Nm) — the twisting force at the crankshaft. Diesel engines favor high torque at low RPM for pulling power. Sports cars favor high RPM for top speed.
• RPM — revolutions per minute of the crankshaft. Horsepower always peaks at higher RPM than torque.
• Horsepower — a rate of doing work; 1 HP = raising 550 pounds by 1 foot in 1 second.

Horsepower to kilowatts conversion: kW = HP × 0.7457

Reference: typical engine outputs

• Economy car (1.5L): 110–130 HP, 130–150 ft-lbs torque
• Midsize sedan (2.5L): 180–205 HP, 180–205 ft-lbs
• Performance car (V8): 400–500 HP, 380–470 ft-lbs
• Heavy diesel truck: 400–600 HP, 900–1,800 ft-lbs (exceptional torque at low RPM)

Worked example: Engine produces 350 ft-lbs of torque at 4,500 RPM.

HP = (350 × 4,500) ÷ 5,252 = 1,575,000 ÷ 5,252 = 299.9 HP ≈ 300 HP

Note: Horsepower and torque curves always cross at 5,252 RPM. Below 5,252 RPM, torque exceeds HP numerically. Above 5,252 RPM, HP exceeds torque. This crossover is a reliable reference point when reading dyno charts.