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