Is the piston on a 4 stroke bigger than stroke 2?

Neither a four stroke nor a two stroke have a bigger piston. It all depends on the size of the engine and how it is built. A 250 four stroke will have the same sized piston that a 250 two stroke would if the bore size is the same. Cc is calculated by bore x stroke (how far up and down the piston moves) so if a 250 four stroke has a stroke of 3.00 inches and a 250 2 stroke has a stroke of 3.00 the piston will be the same size. The only difference between a 2 stroke and four stroke is how the engine works. A 2 stroke has reed valves and it makes power every time the piston goes up but a four stroke it makes power every 4 times the piston goes up.