Abstract: The disclosure defined by this invention utilizes electromagnetic energy reflected from the top and bottom surfaces of ice, the thickness of which is being measured, to determine a phase difference that indicates the thickness of the ice. Since there will be many wave lengths of the electromagnetic energy in the ice, two measurement frequencies are utilized. Integers of wavelengths of each frequency are added to the readings for each frequency to derive sets of numbers. The one number in the set of readings for each frequency that are the same in each set indicate the actual thickness of the ice.