Piston Displacement & Compression Ratio

Method and units

Swept volume per cylinder = π × bore² × stroke ÷ 4. Total displacement multiplies by cylinder count. Geometric compression ratio = (swept volume per cylinder + entered clearance volume) ÷ clearance volume.

Worked example

For an 86 mm bore, 86 mm stroke and four cylinders, total displacement is about 1,998.2 cc. With 50 cc clearance per cylinder, the geometric compression ratio is about 10.99:1.

Supported inputs and interpretation

Bore 20–200 mm; stroke 10–200 mm; integer cylinder count 1–16; clearance 0.1–2,000 cc/cylinder. Results are rounded for display only; internal calculations retain full JavaScript precision. Entered measurements and assumptions determine the answer.

References and limitations

The equations here use the stated unit conversions and geometric or accounting relationships; no empirical vehicle limits or manufacturer presets are supplied.

This ideal geometry excludes deck height, gasket, chamber shape, valve reliefs and measurement tolerances unless already represented in clearance volume. It does not determine dynamic compression, tuning, fuel requirements or modification safety. Verify dimensions with a qualified engine builder.

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This planner performs the stated arithmetic; it is not a vehicle inspection, engineering approval, manufacturer's recommendation or professional review.