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Compression Ratio Calculator
Estimate a cylinder’s static compression ratio from bore, stroke, chamber, gasket, deck and piston-crown measurements. Also calculate total displacement for up to 16 cylinders.
How do I calculate an engine compression ratio?
The static ratio is (swept volume + clearance volume) ÷ clearance volume. Swept volume comes from bore and stroke. Clearance combines chamber, head-gasket, deck and piston-crown volumes. A 9 cc swept volume and 1 cc clearance volume give 10:1.
Frequently asked questions
How do I calculate an engine compression ratio?
The static ratio is (swept volume + clearance volume) ÷ clearance volume. Swept volume comes from bore and stroke. Clearance combines chamber, head-gasket, deck and piston-crown volumes. A 9 cc swept volume and 1 cc clearance volume give 10:1.
Are my engine measurements uploaded?
No. Calculations run in this browser; your measurements are not uploaded or saved.
What is the static compression-ratio formula?
Divide the total volume above the piston at bottom dead center by the clearance volume at top dead center: (swept volume + clearance volume) ÷ clearance volume.
What measurements affect clearance volume?
This estimate combines combustion-chamber volume, compressed head-gasket volume, deck clearance and piston dish or dome volume. A negative deck clearance means the piston rises above the block deck; a dome is entered as a negative piston-crown volume.
Does this tell me whether an engine is safe or will run without knock?
No. It estimates static geometry only. Dynamic compression and detonation also depend on cam timing, fuel, temperature, boost, tuning, materials and engine condition. Check manufacturer specifications and get qualified advice.