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