See also CHP (crankshaft horsepower).
Tuners and enthusiasts typically measure horsepower using a dyno? that measures torque and horsepower at the car’s wheels. These figures are typically 10–20% lower than crankshaft horsepower.
Note that different dynos often yield different measurements for the same car, so quoted wheel horsepower figures are difficult to interpret without a reference. Typically the measured horsepower of the same car in unmodified form is used as a reference.