As time goes by the sea floor is constantly spreading. The movement of the spreading is not very fast, and is normally determined in centimeters per year. To calculate the rate of the spreading, you need to use the following formula: the distance the sea floor moved divided by the length of time. This is an important concept for people in the earth sciences field. To complete these calculations, you will need maps showing the Earth's crust. These help highlight the movement.
Measure from a spot at which the plate is spreading outward to a spot with a known age point.
Use the map's scale to convert the measurement into actual inches of spreading over that time period.
Sciencing Video Vault
Divide the distance the sea floor spread by the time it took to spread that far, to find the rate of spreading per year.