Compression Ratio Calculator
Static compression from chamber, gasket, deck and dome volumes.
Enter your values
Enter the swept volume per cylinder in cc.
Enter the combustion chamber volume in cc.
Enter the head gasket volume in cc.
Enter the deck clearance volume in cc.
Enter the piston dome (−) or dish (+) in cc.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Static compression from chamber, gasket, deck and dome volumes. |
|---|---|
| Category | Auto |
| Inputs needed | Swept volume per cylinder, Combustion chamber volume, Head gasket volume, Deck clearance volume, Piston dome (−) or dish (+) |
| Main output | Compression ratio |
| Formula | CR = (Vswept + Vclearance) ÷ Vclearance |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Swept volume per cylinder(cc)
- Enter the swept volume per cylinder in cc.
- Combustion chamber volume(cc)
- Enter the combustion chamber volume in cc.
- Head gasket volume(cc)
- Enter the head gasket volume in cc.
- Deck clearance volume(cc)
- Enter the deck clearance volume in cc.
- Piston dome (−) or dish (+)(cc)
- Enter the piston dome (−) or dish (+) in cc.
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.
What do I need to enter into the Compression Ratio Calculator?
Just 5 values: swept volume per cylinder, combustion chamber volume, head gasket volume, deck clearance volume, piston dome (−) or dish (+). Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Compression Ratio Calculator work out the answer?
Static compression ratio is (swept volume + clearance volume) ÷ clearance volume, where clearance volume is the chamber, gasket, deck and piston dish combined. It applies the formula CR = (Vswept + Vclearance) ÷ Vclearance and shows the working so you can check each step by hand.
Is the Compression Ratio Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.