There is no guessing when it come to compression ratios. There are so many variables involved. So many people buy pistons off the shelf and believe they will end up with the comp ratio that comes with the piston spec sheet.
There is only one way to calculate it ( it is time consuming and complicated ) and that is why most people and many engine builders evoid it.
Cc'ing piston dome / dish volumes, deck heights ( positive or negative ) , piston valve reliefs, compressed head gaskets ( not the stated thickness ), combustion chambers.
So you can guess, estimate and calculate - but unless you have all those precise measurements you are just walking and talking blind.