Yup!

Stick a wooden dowel down the spark plug hole and measure the stroke.

Then take the muffler off and stick a piece of wood through the exhaust port when the piston is at the bottom. Measure the bore.

CC = stroke X area of the piston.

Area of a circle is 1/2 the diameter times itself. Then times 3.14127

Example:
2" stroke
2.5" bore

1/2 the diameter is 1.25"
1.25 x 1.25 = 1.5625
1.5625 x 3.14127 = 4.908234

4.908234 is the area of the piston in sq. inches

4.908234 x 2 (stroke) = 9.816

That would be 9.816 cubic inches.