Bore, stroke and how displacement is found
The swept-volume formula behind engine size, what square, oversquare and undersquare mean, and how cc, litres and cubic inches relate.
The swept-volume formula
Each cylinder is a circular tube, so the volume a piston sweeps is the area of the bore times the length of the stroke. The bore area is pi divided by 4 times the bore squared, which turns a diameter into a circle's area. Multiply that area by the stroke to get one cylinder's swept volume, then multiply by the cylinder count for the whole engine. Working in millimetres gives cubic millimetres, so the tool divides by 1000 to reach cubic centimetres, the familiar cc.
Square, oversquare and undersquare
The relationship between bore and stroke shapes an engine's character even at the same displacement. A square engine has equal bore and stroke, like the 86 by 86 four in the examples. An oversquare engine has a wider bore than stroke, which lets it spin to higher rpm because the pistons travel a shorter distance each revolution. An undersquare or long stroke engine trades peak rpm for stronger low-end torque and often a narrower, taller block. Designers pick the ratio to suit the vehicle, from high-revving sports engines to torquey trucks.
From cc to litres and cubic inches
Displacement is quoted in different units around the world, so converting matters. Litres are simply cubic centimetres divided by 1000, which is why a 1,998 cc engine is marketed as a 2.0. Cubic inches, common in American muscle car history, come from dividing cc by 16.387064, the number of cubic centimetres in one cubic inch. That is how a 5,733 cc small-block reads as roughly 350 cubic inches, the figure that named a generation of V8s.
What displacement tells you, and what it does not
Displacement sets a rough ceiling on how much air an engine can breathe per cycle, so it correlates with torque and power among similar designs. It does not tell the whole story, because a turbocharger or supercharger forces in extra air, and better cylinder heads, valve timing and higher rpm all raise output for a given size. It also ignores the combustion chamber above the piston, which belongs to the compression ratio instead. Read displacement as a starting point, then let induction and tuning fill in the rest.