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