Engine displacement calculator

Calculate the swept volume of all cylinders from bore, stroke and cylinder count in millimeters or inches.

Formuladisplacement = π ÷ 4 × bore² × stroke × cylinders

A cylinder is a circular area times stroke

The bore supplies the cylinder diameter. Its circular area is multiplied by stroke for one cylinder, then by the number of cylinders for total swept volume.

Nominal and measured dimensions can differ

Published engine size may be rounded. Manufacturing tolerance, wear and an overbore can also make measured dimensions differ from the nominal specification.

Two engines, worked through

A four-cylinder with an 86 mm bore and an 86 mm stroke displaces 499.6 cc per cylinder, so 1,998 cc in total. It will be sold as a 2.0, and that rounding is why the badge on the boot lid rarely matches the arithmetic exactly.

In imperial terms, a small-block V8 with a 4.00-inch bore and a 3.48-inch stroke works out at 5,733 cc, which is 349.9 cubic inches: the engine everyone calls a 350. Bore it 0.030 inches oversize during a rebuild, as countless have been, and it becomes about 355.

Frequently asked questions

Why does my 2.0-litre engine calculate as 1,998 cc?

Because the badge is rounded to the nearest tenth of a litre. Almost no engine lands on a round number: bore and stroke are chosen for the mechanical package, and the displacement falls out of them. Anything within a few cc of the badge is the same engine.

What do oversquare and undersquare mean?

Oversquare means the bore is larger than the stroke, which suits high revs because piston speed stays lower for a given engine speed and there is room for bigger valves. Undersquare, a stroke longer than the bore, favours low-end torque. Square is the two being equal, as in the 86 by 86 example above.

How much does an overbore add?

Less than people expect, because displacement rises with the square of the bore while the extra metal is a thin ring. On a 4.00-inch bore V8, going 0.030 inches oversize adds roughly 5 cubic inches across all eight cylinders, about 1.5%. The point of the overbore is usually to clean up worn or scored cylinders, not to gain capacity.

Should I use nominal or measured dimensions?

Measured, if you have them, and especially on any engine that has been rebuilt. A bore gauge and the actual crank stroke tell you what the engine is now; the catalogue tells you what it was when new. For a stock engine the published figures are close enough for every purpose except a class rule.

Does more displacement mean more power?

It helps, but it settles nothing. Displacement sets how much air the engine can draw per two revolutions; what it does with that air depends on breathing, compression, cam timing, fuel and forced induction. A modern turbocharged 2.0 outproduces plenty of naturally aspirated engines twice its size.