HP to BTU Calculator

This calculator converts horsepower to BTU per hour, the unit used for heating and cooling power. It's handy for comparing engine output, heater capacity, or air-conditioning power on a common scale.

HP to BTU Formula

How to Use This Calculator

1. Enter horsepower.
2. Read BTU per hour.

Worked Example

What a BTU Measures

A BTU (British Thermal Unit) is the energy needed to raise one pound of water by 1°F. BTU per hour is therefore a rate of power, just like horsepower or watts. Heating and cooling equipment — furnaces, boilers, air conditioners — is rated in BTU/hr, so converting from horsepower puts engine or motor output on the same scale as HVAC capacity.

Where HP-to-BTU Is Useful

This conversion helps when sizing the heat output of an engine or motor (for cooling-system design), comparing a generator's power to a heater's rating, or understanding waste heat. Since 1 HP = 2,544.43 BTU/hr = 745.7 W, all three units describe the same power — useful when one device is spec'd in HP and another in BTU/hr.

Shopping for an air conditioner instead? Don't use this page. Room air conditioners are sold on a separate market scale where 1 HP means roughly 9,000 BTU/hr of cooling, so a 12,000 BTU unit is a 1.5 HP model rather than the 4.72 HP the thermodynamic maths gives. Use the aircon BTU to HP calculator for that, or read why the divide-by-9,000 rule drifts above 1 HP.

HP to BTU/hr Conversion Table

Three Different "Horsepowers" Convert to BTU Differently

This is where BTU conversions go badly wrong. The word "horsepower" appears on three unrelated scales, and they differ by more than thirteen times.

Using This for Engine Waste Heat

The most practical use of HP-to-BTU is not comparing an engine with a furnace — it is sizing the cooling system that has to get rid of what the engine wastes.

A piston engine converts only about a quarter to a third of its fuel energy into shaft power. The rest leaves as heat, split roughly evenly between the exhaust and the coolant. As a working approximation:

So a 300 hp engine at full load is pushing on the order of 763,000 BTU/hr into its coolant, with a similar amount going out of the exhaust. That is why a radiator sized for a stock engine becomes marginal the moment power goes up, and why heat rejection — not airflow or fueling — is often what limits sustained output on a modified car.

Treat this as a first-pass figure. Actual heat split varies with load, air-fuel ratio, ignition timing and whether the engine is turbocharged; a manufacturer's heat-rejection data always beats the rule of thumb.

BTU/hr, Tons and Kilowatts Side by Side

Cooling equipment is quoted in whichever unit the market prefers. All four describe the same rate of energy flow:

The fourth column is where the confusion starts: a 12,000 BTU/hr air conditioner is thermodynamically equivalent to 4.7 mechanical horsepower of heat movement, but it is sold as a "1.5 HP" unit and draws barely 1.2 kW of electricity. Three different numbers, one machine — see aircon HP to watts.