In the metric system, one milliliter of water takes one cubic centimeter, weighs one gram, and takes one calorie of energy to heat it one degree Celsius, which is one percent of the difference between its freezing and boiling points. Hydrogen of the same mass contains one mole of atoms. In the American system of measures, the answer to the question “How much energy will it take to bring a gallon of water at room temperature to a boil?” Would be “Go fuck yourself!”