Compression ratio calculator

You need a couple of measurements that are not easy to get in order to calculate your compression ratio, but once you have your figures, here's the calculator. Note that for domed pistons, the "volume" will be a negative number.

Bore	mm
Stroke	mm
Head volume	cc
Piston volume	cc
Gasket thickness	mm
Cylinder volume	cc
Gasket volume	cc
Compression ratio	:1

For example, a four-cylinder motor with a bore of 79.5 mm, a stroke of 86.4 mm, a head volume of 27 cc, a piston volume of 26 cc, and a 1.75 mm thick head gasket will have a compression ratio of 7.95:1.

The formula for compression ratio is:

Compression ratio =	CD + PV + HV + HGV
	PV + HV + HGV

Where:

CD = cylinder displacement
PV = piston volume
HV = cylinder head volume
HGV = head gasket volume