Calculator
Engine Displacement Calculator
Calculate an engine's displacement from bore, stroke and number of cylinders, with the bore/stroke ratio and the mean piston speed at any rpm.
A 3.0-litre 6-cylinder (499 cc each); at 7,000 rpm the pistons average 21.0 m/s.
Drawn to scale0.93 · undersquare (long stroke)
How displacement is calculated
Each cylinder sweeps a cylinder of air: the area of the bore times the stroke. Multiply by the number of cylinders and you have the engine's displacement. BMW's S58 (84.0 × 90.0 mm, six cylinders) works out at 2,993 cc, which is why it is called a 3.0.
Formulas
- cc = π ÷ 4 × bore² (cm) × stroke (cm) × cylinders
- Mean piston speed (m/s) = 2 × stroke (m) × rpm ÷ 60
Oversquare, square and undersquare
A bore larger than the stroke (oversquare) means shorter piston travel and room for bigger valves, so the engine revs freely: Ferrari and Honda VTEC engines are typical. A long stroke (undersquare) gives strong low-down torque and a compact combustion chamber, as in most modern turbo four-cylinders and diesels.
Mean piston speed limits how high an engine can safely rev. Road engines sit around 20-25 m/s at the redline, Formula 1 engines reached 25-26 m/s. A long stroke reaches that limit at lower rpm.
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