I usually just use a metric conversion calculator to convert for sizes I am not sure of.

http://www.sciencemadesimple.com/volume_conversion.php


usually things like
1.5cc = .09 cubic inches
2.5cc = .15 cubic inches
3.5cc = .21 cubic inches.
a 6.5cc = .40 cubic inches.
a 10cc = .61 cubic inches.
a 20cc = 1.2 cubic inches
a 30cc = 1.8 cubic inches
a 40cc = 3 cubic inches.