G'day Mel, welcome to the forum.
Also look inside the piston for make or casting #'s then google.
The other way is a bit messy, but the one I use, is to cc the combustion chamber. With the piston on TDC comp stroke lean bike over till the spark plug hole is vertical, then using a syringe accurately measure how much oil it takes to reach the bottom of the spark plug thread. I do this to make sure both cylinders are the same. Swept vol of cyl + your cc / your cc = comp.
Cheers
Just saw manosound's. I got 10.5:1 in the cafe, but I'm still a month away from 50.