Engine Performance Calculator
Calculate engine horsepower from torque and RPM using HP = torque × RPM / 5252. Use this to understand your engine's peak power output or compare different builds.
Last updated: September 2026
Formula below · 2 sources (nhtsa.gov, Wikipedia) · Updated Sep 2026
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About this calculator
The fundamental relationship between horsepower and torque is defined by the physics of rotational work. The standard formula is: HP = (Torque × RPM) / 5252, where 5252 is a constant derived from unit conversions (one horsepower equals 33,000 foot-pounds per minute, divided by 2π). This relationship is exact: the torque you enter already reflects the engine's displacement and any turbo or supercharger boost, so no further adjustment is needed. A 300 lb-ft engine at 4,000 RPM makes 228.5 HP whether it is a naturally aspirated 5.0 L or a turbocharged 2.0 L. The displacement and aspiration inputs are for reference and do not change the result; to estimate what adding boost would do, use the turbo boost calculator. Real-world dyno figures vary with engine condition, altitude and temperature, and wheel horsepower is typically 10-20% below crank horsepower because of drivetrain losses.
How to use
Suppose your engine produces 300 lb-ft of torque at 4,500 RPM. HP = (300 × 4,500) / 5252 = 1,350,000 / 5252 ≈ 257.0 HP. That is the power at 4,500 RPM specifically; to find peak horsepower, repeat the calculation with the torque reading at each RPM on the dyno chart and take the highest result.
Frequently asked questions
What is the formula for converting torque and RPM to horsepower?
The standard conversion is HP = (Torque in lb-ft × RPM) ÷ 5252. The constant 5252 comes from dividing 33,000 (foot-pounds per minute in one horsepower) by 2π (to convert from linear to rotational work). This formula is used by SAE, dyno operators, and engineers worldwide and is accurate for any internal combustion engine regardless of cylinder count or configuration.
How does forced induction (turbo or supercharger) increase horsepower?
Forced induction compresses the intake air before it enters the combustion chamber, allowing more oxygen — and therefore more fuel — to be burned per cycle. This increases the torque output at each RPM, which directly raises horsepower by the HP = Torque × RPM / 5252 relationship. A well-tuned turbocharger can increase an engine's power output by 30–50% or more over its naturally aspirated baseline without significantly increasing engine displacement.
Why does peak horsepower occur at a different RPM than peak torque?
Torque is a measure of twisting force at any given moment, and it typically peaks at lower to mid RPM where the engine's breathing efficiency and combustion pressure are optimized. Horsepower is a rate of doing work — it is torque multiplied by how fast that torque is being applied — so it continues to rise as RPM increases even after torque begins to fall. The RPM at which the torque and horsepower curves cross is always exactly 5252, which is a direct consequence of the conversion formula.