Standard gasket thickness is 0.7mm
Right if the standard compression ratio on my ej257 is
Compression 8.2 ± 0.2

and I fit Mahle Forged Pistons with a COMPRESSION HEIGHT of 1.209" AND 22cc BOWL VOLUME.

what thickness cometic steel headgaskets do I fit to keep within the standard Ratio Range ??

 

Assuming your heads and block deck faces have not been skimmed, then your measured standard head gasket thickness of 0.7mm would give you a static CR of 8.33:1.
Always best to do a dry build of the block to measure the deck height clearance of the pistons and then volume the combustion chambers to confirm and determine your final gasket thickness.
I think the EJ257 heads come out at approx. 54cc ( but thats on a sunday afternoon after a few beers lol ).


Mick