Engine Compression Calculator

Compression ratio basics

Compression ratio = (swept volume + clearance volume) ÷ clearance volume. It tells how much the fuel-air charge is squeezed before ignition.

• Typical petrol engines : 9.0:1 to 12.5:1
• Turbo petrol engines : 8.5:1 to 10.5:1 (boost needs lower static ratio)
• Diesels : 16:1 to 22:1
• Higher ratio = more efficiency and torque, but requires higher-octane fuel