Grams per gallon (US) to milligrams per liter converter above calculates how many milligrams per liter are in 'X' grams per gallon (US) (where 'X' is the number of grams per gallon (US) to convert to milligrams per liter). In order to convert a value from grams per gallon (US) to milligrams per liter (from g/gal to mg/L) type the number of g/gal to be converted to mg/L and then click on the 'convert' button.