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Engine Compression Ratio Calculator — result sheet
Calculate swept displacement, total cylinder volume, and nominal static compression ratio from bore, stroke, cylinder count, and clearance volume.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Swept volume per cylinder = π(bore/2)² × stroke; total cylinder volume = swept volume + clearance volume; nominal compression ratio = total cylinder volume ÷ clearance volume.
Static compression ratio compares the cylinder volume at the piston bottom position with the clearance volume at the top position. The page keeps per-cylinder and total displacement visible and does not confuse nominal compression ratio with dynamic valve-timing compression or a performance recommendation.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Cylinder bore — mm; minimum 1.0E-6; maximum 1000000
- Piston stroke — mm; minimum 1.0E-6; maximum 1000000
- Number of cylinders — minimum 1; maximum 1000
- Clearance volume per cylinder — cm³; minimum 1.0E-6; maximum 1000000000
Worked example
| Input | Value |
|---|---|
| Cylinder bore | 86 |
| Piston stroke | 86 |
| Number of cylinders | 4 |
| Clearance volume per cylinder | 50 |
Swept volume ≈499.56 cm³ per cylinder; total displacement ≈1,998.24 cm³; compression ratio ≈10.991:1.
Assumptions and limits
- Bore and stroke are cylindrical dimensions and are converted from millimetres to cubic centimetres.
- All cylinders are treated as identical and the entered clearance volume applies to each cylinder.
- The result is a nominal static compression ratio, not an effective ratio based on intake-valve closing.
- Combustion-chamber shape, gasket volume, deck clearance, piston dish or dome, and measurement uncertainty are represented only through the entered clearance volume.
- The calculator does not determine fuel suitability, detonation risk, ignition timing, engine durability, or legal compliance.
- A ratio is dimensionless and is reported as a number with a planning colon form.
- Use measured component volumes and qualified engine-building review for a real build or modification.
- Non-cylindrical or variable-compression designs need a more detailed model.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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