Horsepower-hour to watt hours conversion calculator shown above calculates how many watt hours are in 'X' horsepower-hour (where 'X' is the number of horsepower-hour to convert to watt hours). In order to convert a value from horsepower-hour to watt hours (from hph to Wh) simply type the number of hph to be converted to Wh and then click on the 'convert' button.