Gallon-atmosphere (US) to calories converter above calculates how many calories are in 'X' gallon-atmosphere (US) (where 'X' is the number of gallon-atmosphere (US) to convert to calories). In order to convert a value from gallon-atmosphere (US) to calories (from gal atm to cal) type the number of gal atm to be converted to cal and then click on the 'convert' button.