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Automotive Calculators

Compression Ratio Calculator

Verified formula Updated Jun 2026 Private — runs on your device

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cc
cc
Verified formula Private

Compression ratio (to 1)

11.00

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Compression Ratio Calculator

The Compression Ratio Calculator works out your compression ratio (to 1) in an instant. Enter cylinder (swept) volume and clearance volume and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the cylinder (swept) volume.
  2. Enter the clearance volume.
  3. Read off your compression ratio (to 1) — the calculator updates automatically, with no button to press.

Formula

The Compression Ratio Calculator uses the formula:

Compression ratio (to 1) = (Cylinder (swept) volume + Clearance volume) ÷ Clearance volume

Worked example

For example, with cylinder (swept) volume of 500 cc and clearance volume of 50 cc, the compression ratio (to 1) is 11.00.

Inputs used
Cylinder (swept) volume 500 cc
Clearance volume 50 cc
Results
Compression ratio (to 1) 11.00

Results are estimates for educational use, not professional advice.

Key terms explained

Volume
The amount of three-dimensional space an object occupies, measured in cubic units.
Ratio
A comparison of two quantities showing how many times one contains the other.

Frequently asked questions

Add the swept and clearance volumes, then divide by the clearance volume. A 500 cc cylinder with 50 cc clearance is an 11:1 ratio.

It is how much the air-fuel mixture is squeezed before ignition. A higher ratio generally improves efficiency and power.

Petrol engines are often around 9:1 to 12:1, while diesels run much higher, around 15:1 to 22:1.

Yes. Too high a ratio for the fuel causes knocking. Higher ratios usually need higher-octane fuel to run safely.

Enter the cylinder (swept) volume. Enter the clearance volume. Read off your compression ratio (to 1) — the calculator updates automatically, with no button to press.

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