Engine Displacement Calculator
Works out engine capacity from bore, stroke and cylinder count, in cc, litres and cubic inches, and shows what a rebore adds.
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The formula
displacement = π⁄4 × bore² × stroke × cylinders
Each cylinder sweeps a cylinder of volume π r² h — the piston area times the stroke. Bore enters squared, which is why a small overbore adds little and why engines of the same displacement with different bore-stroke ratios behave so differently.
What to watch out for
What the bore-to-stroke ratio tells you:
- Oversquare (bore larger than stroke) — lower piston speed at a given rpm, room for big valves, so it revs. Sports and motorcycle engines.
- Undersquare (stroke larger) — more leverage on the crank, better low-rpm torque, longer and narrower. Diesels, economy engines.
A stroker crank changes displacement linearly with stroke; a rebore changes it with the square of bore. 0.5 mm on an 86 mm bore is only 1.2% more capacity — rebores are for restoring a worn bore, not for adding power.
Frequently Asked Questions
How do I calculate engine displacement?
π⁄4 × bore² × stroke × number of cylinders, in millimetres, then divide by 1,000 for cc. An 86 × 86 mm four-cylinder is 1,998 cc — the classic 2.0 litre.
How many cc is a litre?
1,000. And a litre is 61.02 cubic inches, so a 5.7 litre V8 is 350 cubic inches — give or take the rounding manufacturers apply.
How much does an overbore add?
Very little. Displacement goes with bore squared, so a 0.5 mm oversize on an 86 mm bore adds about 1.2%. It is done to clean up a worn cylinder, not for performance.