Millimeters per second to feet per second conversion calculator above calculates how many feet per second are in 'X' millimeters per second (where 'X' is the number of millimeters per second to convert to feet per second). In order to convert a value from millimeters per second to feet per second (from mm/s to ft/s) simply type the number of mm/s to be converted to ft/s and then click on the 'convert' button.