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Compression Ratio Calculator
Calculate static compression ratio from engine volumes
Static compression ratio compares cylinder volume with the piston at the bottom of the stroke to its volume at the top.
Formula: CR = (swept volume + clearance volume) ÷ clearance volume; clearance = chamber + gasket + deck + piston volume
What this number means
This calculates static compression ratio from bore, stroke, chamber volume, piston dish or dome, deck height and gasket thickness. It is the geometric ratio machined into the engine, before the camshaft has any say.
What to change next
Use it to verify a build on paper before parts are ordered — small chamber or gasket changes move the ratio meaningfully. Match the result to your fuel: pump gasoline, E85 and race fuel each have sensible ranges.
Worked example
A 4.030 in bore, 3.48 in stroke V8 cylinder with a 64 cc chamber, flat-top piston and typical gasket and deck volumes gives ≈ 10.2:1.