Gigapascals to newtons per square millimeter conversion calculator above calculates how many newtons per square millimeter are in 'X' gigapascals (where 'X' is the number of gigapascals to convert to newtons per square millimeter). In order to convert a value from gigapascals to newtons per square millimeter (from GPa to N/mm²) simply type the number of GPa to be converted to N/mm² and then click on the 'convert' button.