Horsepower (or "HP") is the unit of measurement that describes the power of engines in various machines. However, there are various types of horsepower measurements, including the DIN HP (a version of horsepower that is measurement protocol in Germany) and SAE (which is the standard definition of horsepower). While the two measurements are close, the difference is enough that it must be calculated.
Find the DIN HP. If you are finding this manually, measure the horsepower at the point of the engine's output. This is different from SAE horsepower because that is measured at the flywheel point of the engine.
Divide the DIN HP by 1.0139 to find the SAE. This is to account for the small difference between testing methods.
In most cases, the difference in DIN HP and SAE is so negligible that the two numbers are interchangeable and engineers don't use the formula to find the actual difference.