BHP

Brake horsepower (bhp) is a unit used to express the power output of an internal combustion engine. It measures the engine’s power at the crankshaft as the engine drives a brake on a dynamometer, representing the usable power available to the drivetrain before losses in the transmission and wheels are encountered.

Measurement and standards

Bhp is determined on a brake dynamometer, where the engine is tested in controlled conditions and subjected to a resistance that simulates loading. The torque and rotational speed are recorded, and horsepower is calculated. Test conditions—such as ambient temperature, altitude, humidity, and accessory loads—can affect the result, and various standards (for example SAE and ISO) exist to specify test procedures and correction factors.

Relation to other power figures

Horsepower has many variants. Bhp (often used in the UK and other markets) is typically close to the engine’s rated output, while wheel horsepower measures power at the wheels after drivetrain losses. Indicated horsepower describes the engine’s theoretical output from cylinder pressures inside the engine. In metric terms, 1 brake horsepower equals about 0.7457 kilowatts; 1 metric horsepower (PS) equals about 0.7355 kilowatts.

History and usage

The term brake horsepower originated in the era of friction brakes used on engine test stands. The phrase “brake” distinguishes the measured power from theoretical or wheel-based figures. Today bhp remains a common some-market specification for internal combustion engines, though many regions prefer kilowatts or metric horsepower on official documentation and advertising.

Notes

Published bhp values can vary between manufacturers and testing setups. For precise comparisons, consider the stated standards, testing conditions, and whether the value is bhp, wheel horsepower, or another metric.