How Motorcycles Work.com engine mathematics bore size diameter of cylinder top of piston travel stroke length bottom of piston travel crank throw length distance from center of crankpin to center of crankshaft crankshaft journal diameter engine displacement = pi or 3.14159 x bore size / 2 squared x stroke length x number of cylinders example 1995 kawasaki klx 650 single cylinder bore and stroke 100 x 83 mm displacement = 3.14159 x 100 / 2 squared x 83 x 1 = 3.14159 x 2500 x 83 = 651879 mm cubed = 651 cm cubed 1000 mm cubed = 1 cm cubed cm cubed = cc = cubic centimeter mm cubed = cubic millimeter in cubed = cubic inch example 2001 Yamaha YZF-R6 four cylinder bore and stroke 65.5 x 44.5 mm 2.58 in x 1.75 in displacement = 3.14159 x 65.5 / 2 cubed x 44.5 x 4 = 599780 mm cubed = 600 cm cubed 600 cc displacement = 3.14159 x 2.58 / 2 cubed x 1.75 x 4 = 36.595 in cubed cubic inches = 599684 cm cubed = 600 cm cubed cc 1 in cubed cubic inch = 2.54 cubed cm cubed cubic cm 1 in cubed = 16.387 cm cubed compression ratio e.g.: 12.5:1 relative volume space that fuel/air mixture is compressed to a.k.a. it was compressed to 1/12.5 times its starting volume when it reaches tdc : volume of air in combustion chamber and cylinder right before intake valves close 4-stroke, right before piston covers exhaust port openings and intake port openings 2-stroke piston port right before rotary valve closes 2-stroke rotary valve actually these definitions are reversed