Compression Ratio Calculator

cc
cc
Physics

The Compression Ratio Calculator finds an engine's compression ratio from the cylinder (swept) volume and the clearance (combustion chamber) volume.

Formula

Compression Ratio = (Swept Volume + Clearance Volume) ÷ Clearance Volume
  • Swept volume is the cylinder displacement; clearance volume is the space left at top dead centre.
  • Higher compression ratios generally improve efficiency but need higher-octane fuel.

500 cc swept, 50 cc clearance

Inputs
  • Swept Volume: 500 cc
  • Clearance Volume: 50 cc

(500 + 50) ÷ 50 = 11.0, i.e. an 11:1 compression ratio.

Frequently asked questions

What is a good compression ratio?
Everyday petrol engines run about 9:1 to 11:1; performance engines may go higher with premium fuel.