HP & RPM Relationship Calculator
See how horsepower changes with RPM at constant torque, and what 1 HP means at a given RPM.
Horsepower and RPM are tied together through torque. This calculator shows how horsepower rises with engine speed for a given torque, and illustrates why RPM is half of the horsepower equation.
The HP–RPM Relationship
This is why engines make peak horsepower high in the rev range even though torque often peaks much lower: as RPM climbs, each unit of torque produces more horsepower. At exactly 5252 RPM, the horsepower and torque numbers are equal.
How to Use This Calculator
- Enter torque in lb-ft.
- Enter RPM.
- See the horsepower that combination produces.
Worked Example
Frequently Asked Questions
Horsepower equals torque times RPM divided by 5252. For a fixed torque, horsepower increases directly with RPM.
Because horsepower multiplies torque by RPM. Even as torque falls off at high RPM, the rising RPM can keep increasing horsepower until torque drops too steeply.
Rearranging the formula, torque = (1 × 5252) ÷ RPM. At 5252 RPM, 1 HP equals 1 lb-ft; at 2626 RPM it equals 2 lb-ft.
At 5252 RPM the formula's multiplier becomes 1, so horsepower and torque are numerically equal. It comes from 33,000 ÷ 2π.
Only if torque holds up. Horsepower rises with RPM until torque falls faster than RPM increases, which sets the power peak.