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