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