How to Check Compression

anyone care to take a poke at the math part of this for me?

I'm totally lost on the calculations. I pulled the heads off my 318 just to get these measurements.

Bore 3.940" - .030 over 318

stroke 3.31" - standard 318

combustion chamber 65cc

piston to deck volume 10cc

head gasket is .050" thick

head gasket opening size is 4.1875"

a little help here would be great!

8.78:1