Calculating your compression ratio (to 1) is straightforward once you know the Compression Ratio formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Compression Ratio Calculator.
What is Compression Ratio?
The Compression Ratio calculation tells you your compression ratio (to 1) from a few simple inputs. The figure you are solving for here is the compression ratio (to 1).
The Compression Ratio formula
The core formula is:
Compression ratio (to 1) = (Cylinder (swept) volume + Clearance volume) ÷ Clearance volumeHere is what each input means:
- Cylinder (swept) volume — a value measured in cc. Example: 500 cc.
- Clearance volume — a value measured in cc. Example: 50 cc.
How to calculate it step by step
- Write down the cylinder (swept) volume (for example, 500 cc).
- Write down the clearance volume (for example, 50 cc).
- Apply the formula above to get your compression ratio (to 1).
- Double-check the result with the Compression Ratio Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Cylinder (swept) volume | 500 cc |
| Clearance volume | 50 cc |
| Compression ratio (to 1) | 11.00 |
With cylinder (swept) volume of 500 cc and clearance volume of 50 cc, the compression ratio (to 1) works out to 11.00.
Example 2
With cylinder (swept) volume of 1,000 cc and clearance volume of 50 cc, the compression ratio (to 1) works out to 21.00.
| Result | Value |
|---|---|
| Compression ratio (to 1) | 21.00 |
Example 3
With cylinder (swept) volume of 250 cc and clearance volume of 50 cc, the compression ratio (to 1) works out to 6.00.
| Result | Value |
|---|---|
| Compression ratio (to 1) | 6.00 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Compression Ratio Calculator does it instantly, for free, with the formula and a worked example built in.
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