Engine Horsepower Calculator
Calculate engine horsepower based on displacement, RPM, and efficiency
Horsepower
115.9 kW
Torque
201 Nm
Power to Weight
22.5 lbs/HP
Est. 0-60 mph
Rough estimate
Engine Analysis
Performance Categories
Specific Output (HP/L)
Power to Weight (HP/lb)
How it works
Horsepower measures an engine's rate of doing work. It's derived from torque (twisting force) and engine speed (RPM): the faster an engine spins at a given torque, the more power it makes. The constant 5252 comes from the definition of horsepower.
Horsepower from torque & RPM
HP = (torque × RPM) ÷ 5252
- torque
- in lb-ft
- RPM
- engine revolutions per minute
Worked example
- Torque = 300 lb-ft
- At 5,000 RPM
- HP = (300 × 5000) ÷ 5252
≈ 286 horsepower.
Good to know
- Torque and horsepower curves always cross at 5,252 RPM — that's where the formula's constant lands.
- Torque is the pulling force; horsepower is how quickly that force does work.
- Quoted 'crank' horsepower is higher than 'wheel' horsepower, which loses some to the drivetrain.
Related Calculators
Frequently Asked Questions
How does this calculator estimate engine horsepower?
It uses the standard relationship between torque and engine speed: HP = (torque × RPM) ÷ 5252, with torque in lb-ft. Methods based on displacement and volumetric efficiency estimate airflow first, since power is ultimately limited by how much air and fuel the engine can burn.
What's the difference between crank horsepower and wheel horsepower?
Crank (brake) horsepower is measured at the engine's output shaft, while wheel horsepower is measured after the drivetrain. Expect roughly 10-15% loss through a manual transmission and 15-25% through automatics and all-wheel-drive systems.
Why do torque and horsepower curves always cross at 5,252 RPM?
Because of the constant in the formula HP = torque × RPM ÷ 5252. At exactly 5,252 RPM the equation forces horsepower and torque (in lb-ft) to be numerically equal, so the curves intersect there on every dyno chart.
What is volumetric efficiency?
Volumetric efficiency (VE) measures how completely the cylinders fill with air on each intake stroke. Naturally aspirated engines typically run 80-100% VE, while turbocharged or supercharged engines can exceed 100% because the intake charge is force-fed.
Does altitude or weather affect horsepower?
Yes. Thinner air at altitude means less oxygen per intake stroke — a naturally aspirated engine loses roughly 3% of its power per 1,000 feet of elevation. Hot, humid air also reduces air density and therefore power.