Engine Compression Ratio Calculator

Calculate your engine's compression ratio based on cylinder volume, combustion chamber volume, and other factors.

Reviewed August 29, 2026 · Calculation methodology · Inputs stay in your browser

Cylinder Bore Enter the cylinder bore diameter.

Piston Stroke Enter the piston stroke length.

Combustion Chamber Volume Enter the combustion chamber volume.

Piston Top Volume Enter negative for dome pistons, positive for dish pistons.

Head Gasket Thickness Enter the compressed head gasket thickness.

Head Gasket Bore Enter the head gasket bore diameter (typically slightly larger than cylinder bore).

Deck Clearance Enter the distance from the piston top to block deck at TDC (positive if below, negative if above).

Compression Ratio Tips

Compression ratio = (Swept volume + Clearance volume) ÷ Clearance volume
Higher compression ratios generally increase power and efficiency but require higher octane fuel.
Turbocharged or supercharged engines typically use lower compression ratios.
Typical compression ratios: Regular gas engines: 8:1 to 10:1, Premium gas engines: 10:1 to 12:1, Race engines: 12:1 to 16:1
Dome pistons increase compression ratio, while dish pistons decrease it.
A thinner head gasket increases compression ratio, while a thicker one decreases it.