If you have the bore size, rod stroke length, and the number of cylinders you can calculate the displacement of the engine in question. Bore size is the diameter of the cylinder. The stoke length is how far the rod moves within the cylinder. The cylinder count is self-explanatory. Simply plug the numbers into the calculator, select Solve and the displacement appears in inches and centimeters below. This is a great way to figure out the size of an engine build project prior to ordering parts.