HP to ft-lb/min Calculator

This converter shows horsepower in foot-pounds per minute — the exact unit James Watt used when he defined one horsepower as 33,000 foot-pounds of work per minute.

HP to ft-lb/min Formula

This is where horsepower comes from. Watt measured that a horse could do roughly 33,000 foot-pounds of work each minute. That figure became the definition of one horsepower. It's also why the constant 5252 (33,000 ÷ 2π) turns up in the torque formula.

How to Use This Calculator

1. Enter horsepower.
2. Read ft-lb/min, with ft-lb/sec also shown.

Worked Example

The Origin of Horsepower

In the 1780s James Watt needed a way to market his steam engines against the draft horses they replaced. He measured that a strong horse could do about 33,000 foot-pounds of work per minute — lifting 33,000 pounds one foot, or 330 pounds 100 feet, in sixty seconds — and named that rate one horsepower. Every modern horsepower figure still traces back to this benchmark, which is why the unit feels arbitrary until you see its origin.

Why 33,000 Leads to 5252

This definition is the source of the famous 5252 constant in the torque equation. Since power = torque × angular velocity, and one revolution is 2π radians, dividing 33,000 by 2π gives 5,252 — the RPM at which horsepower and torque are numerically equal. The same 33,000 ft-lb/min also equals 550 ft-lb/sec and 745.7 watts.

HP to ft-lb/min and ft-lb/sec

What James Watt Actually Measured

The 33,000 figure has a specific origin, and it isn't a physical constant so much as a marketing decision that happened to stick for 250 years.

Watt needed a way to sell steam engines to mill owners who were already using horses, which meant expressing his engines in units the buyer already understood. Observing horses turning a mill wheel, he measured a horse walking a circle of roughly 24 feet in diameter, completing about 2.5 turns per minute while pulling against a load of around 180 pounds. That works out to roughly 32,400 foot-pounds per minute, which he rounded to 33,000.

The unit outlived the reasoning entirely. It now describes aircraft engines, electric motors and industrial pumps in situations where no horse was ever involved, which is why the number looks so arbitrary today. Everything downstream — the 550 ft-lb/sec figure, the 745.7 watt equivalence, even the 5252 constant on dyno charts — traces back to that observation of a horse walking in a circle.

The Complete Power Unit Family

Foot-pounds per minute sits in a family of work-rate units that all express the same physical quantity in different bases:

The last row is a trap worth knowing about. Metric horsepower was defined independently as 75 kilogram-force meters per second, which comes out slightly smaller than mechanical horsepower — 735.5 watts against 745.7. Quoting a European PS figure as though it were mechanical horsepower overstates it by about 1.4%. The HP to PS converter handles that difference properly, and the HP to BTU calculator covers the thermal row.

Where Foot-Pounds Per Minute Is Genuinely the Right Unit

For most modern purposes horsepower or kilowatts are more convenient. Foot-pounds per minute earns its place in one specific situation: any job defined as lifting a known weight at a known speed, where the arithmetic works out directly with no constant to remember.

Take a hoist required to lift 2,000 pounds at 30 feet per minute. The work rate is simply the weight multiplied by the speed:

That 1.82 HP is what reaches the hook, not what the motor must produce. A gearbox, cable drum and sheaves together typically run 65 to 80% efficient. So you need about 2.6 HP at the motor to deliver it. In practice you'd specify the next standard size up: a 3 HP unit. Sizing the motor at 1.82 HP would leave it permanently overloaded.

Compare the third and fourth rows. Doubling the load while halving the speed needs exactly the same power, which is the clearest possible demonstration that power is a rate rather than a quantity. The gearing changes, the torque at the drum doubles, but the motor size doesn't move. Convert any of these into metric with the HP to kW calculator.