Engine Compression Ratio Calculator

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

Enter the cylinder bore diameter.
Enter the piston stroke length.
Enter the combustion chamber volume.
Enter negative for dome pistons, positive for dish pistons.
Enter the compressed head gasket thickness.
Enter the head gasket bore diameter (typically slightly larger than cylinder bore).
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.

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