Wankel engines can be classified by their geometric size in terms of radius (rotor center to tip distance, also the median stator radius) and depth (rotor thickness), and offset (crank throw, eccentricity, also 1/4 the difference between stator's major and minor axes). These metrics function similarly to the bore and stroke measurements of a piston engine. Displacement = (3*3^(1/2) Depth*Radius^2 (Offset/Radius))/1,000, multiplied with the number of rotors (note that this only counts a single face of each rotor as the entire rotor's displacement, because with the eccentric shaft – crankshaft – spinning at three times the rate of the rotor, only one power stroke is created per output revolution, thus only one face of the rotor is actually working per "crankshaft" revolution, roughly equivalent to a 2-stroke engine of similar displacement to ONE rotor face). Nearly all Mazda production Wankel engines share a single rotor radius, , with a crankshaft offset. The only engine to diverge from this formula was the rare 13A, which used a rotor radius and crankshaft offset.