Hi Folks,
Technically, it is called the "swept volume", which is, as previously said, the bore area multiplied by the piston stroke. (i.e. bore dia squared multiplied by Pi, divided by 4, and that result multiplied by the maximum travel of the piston - keeping the units the same - inches or metric).
Oh, and the above multiplied by the number of cylinders if more than one.....
Happy motoring (or flying!)
Cheers
Harry
forgot to mention - original engines tend to be smaller to allow for first rebore, so the engine does not go above the original quoted capacity.