Compression Ratio Calculator
Static compression from chamber, gasket, deck and dome volumes.
Enter your values
ⓘ Live results
- Compression ratio
- 9.33:1
- Clearance volume
- 60 cc
- Fuel guide
- Regular pump fuel is fine
- Dynamic estimate
- 7.93:1 (typical cam bleed-off)
Quick answer
Static compression ratio is (swept volume + clearance volume) ÷ clearance volume, where clearance volume is the chamber, gasket, deck and piston dish combined.
CR = (Vswept + Vclearance) ÷ Vclearance
How to use the Compression Ratio Calculator
- 1Enter swept volume per cylinder (displacement ÷ cylinders).
- 2Add chamber, gasket and deck clearance volumes in cc.
- 3Enter piston dome as a negative number and a dish as positive.
Worked example
Using the values the calculator loads with:
Inputs
- Swept volume per cylinder500 cc
- Combustion chamber volume50 cc
- Head gasket volume8 cc
- Deck clearance volume2 cc
- Piston dome (−) or dish (+)0 cc
Results
- Compression ratio9.33:1
- Clearance volume60 cc
- Fuel guideRegular pump fuel is fine
- Dynamic estimate7.93:1 (typical cam bleed-off)
Frequently asked questions
What compression ratio needs premium fuel?
Naturally aspirated engines above roughly 10.5:1 usually need premium to avoid knock, though direct injection and modern knock sensors push that higher.
Why is dynamic compression lower?
The intake valve stays open past bottom dead centre, so part of the charge is pushed back out and the effective ratio drops — typically 10–20% below static.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.