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