Engine Horsepower Calculator

Engine horsepower can be calculated from several measurable quantities. The most direct method uses torque and RPM — two values readable from a dynamometer:

HP = Torque (lb·ft) × RPM / 5,252

The constant 5,252 comes from unit conversion: 1 horsepower = 550 ft·lbs/second, and one revolution involves 2π radians.

From engine displacement and mean effective pressure (theoretical):

HP = BMEP (psi) × Displacement (in³) × RPM / (792,000 × Stroke Cycles)

For a 4-stroke engine: HP = BMEP × L × n / 792,000 (where n is RPM/2 for 4-stroke firing)

From fuel consumption (brake-specific fuel consumption method):

HP = Fuel Flow (lb/hr) / BSFC

Typical BSFC for gasoline engines: 0.40–0.55 lb/hp·hr

Worked Example — Using torque/RPM:

• Dyno shows peak torque: 275 lb·ft at 4,200 RPM
• HP = 275 × 4,200 / 5,252 = 219.8 HP
• Peak HP often occurs at a different (higher) RPM than peak torque

Example 2 — From fuel flow:

• Engine burns 22 lb/hr of gasoline at wide-open throttle
• BSFC = 0.45 lb/hp·hr
• HP = 22 / 0.45 = 48.9 HP (small engine example)

Power Unit Conversions:

• 1 HP = 745.7 Watts
• 1 HP = 0.7457 kW
• 1 kW = 1.341 HP

Reference: A typical family sedan produces 150–200 HP; performance cars 300–500 HP; supercars 600–1,000 HP. NASCAR engines generate ~900 HP from 5.86L naturally aspirated V8s.