[Duffy.yyz]

I have to replace pistons in a 25hp Tohatsu. I know it has had some modifications to it, but I do not know if the cylinders have been messed with....I am ordering the pistons and doing it myself. This may be a dumb question, but is there anyway to measure the cylinder to see what size pistons I need? I wasn't sure how they sized pistons. Thanks in advance for any input guys, I appreciate it.