Horsepower Calculator

Horsepower equals torque in pound-feet times engine speed in rpm, divided by the constant 5252. Rearranged, torque equals hp times 5252 divided by rpm, and rpm equals hp times 5252 divided by torque.

One horsepower is defined as 33,000 pound-feet of work per minute. Converting torque and rpm to that basis divides by 2 times pi, and 33,000 divided by 6.2832 is about 5252.

Because horsepower equals torque times rpm over 5252, the two values are numerically equal exactly at 5252 rpm. On a dyno chart with a shared axis, the curves therefore always intersect at that engine speed.

No. Pick one value in the Solve for menu and provide the other two. That box is disabled and the calculator fills in the missing third value.

The formula does not care; it converts whatever torque and rpm you feed it. Use crank figures for engine output, or wheel figures from a chassis dyno for power at the tires after drivetrain loss.

Torque in pound-feet and speed in rpm, not Newton-meters or kilowatts. To convert torque, divide Newton-meters by 1.3558 to get pound-feet. To convert the result, multiply horsepower by 0.7457 to get kilowatts.

Yes. Set the Solve for menu to Torque or RPM. Enter the two known values and the tool rearranges the same equation to return the one you left out.

Yes, the relationship is pure math and holds at any instant. Keep in mind that electric motors make near flat torque from zero, so their peak horsepower still arrives at higher rpm just as the formula predicts.

The calculation is exact. The display rounds horsepower and torque to two decimals and rpm to the nearest whole number, so tiny rounding at the last digit is expected.