Compression ratio calculator

Static compression ratio is the cylinder's full volume at bottom dead center divided by its clearance volume at top dead center. The swept volume comes from bore and stroke; the clearance volume is the sum of combustion chamber, head gasket bore × thickness, deck clearance, and piston dish (add) or dome (subtract). Small clearance-volume changes move CR a lot — which is exactly how a thinner gasket or a skim cut raises compression.