Engine Displacement Calculator

Bore, mm

Stroke, mm

Cylinders

Combustion chamber, cc

Only needed for the compression ratio.

Result

Displacement, cc1,816.7
In litres1.82
Per cylinder, cc454.2
Bore to stroke ratio0.953
Engine charactersquare: an all-rounder
Compression ratioenter the chamber volume

Piston area times stroke, and that is all

Works out engine displacement from bore, stroke and cylinder count, and adds the compression ratio when the chamber volume is known.

Displacement is the area of the piston multiplied by the distance it travels between top and bottom dead centre, multiplied by the number of cylinders. That is where the tidy '1.6' and '2.0' on the bootlid come from, even though the real figure is almost never round.

The ratio of bore to stroke says as much about an engine's character as its capacity. An oversquare motor revs freely and makes its power high up; an undersquare one pulls from low down and dislikes revs — at identical capacity, two very different cars.

What this calculator shows

Displacement in cubic centimetres and in litres
The volume of a single cylinder and the bore-to-stroke ratio
The compression ratio, if the combustion chamber volume is known

What to keep in mind

The geometry ignores piston crown dishes and gasket volume — an accurate compression ratio needs those measured separately.
The boundaries are conventional: above 1.05 counts as oversquare, below 0.95 as undersquare.

FAQs

How do I calculate engine displacement?

Multiply the cylinder area by the stroke and by the number of cylinders. The area is pi over four times the bore squared.

Why is the advertised capacity round and the calculated one not?

Because the manufacturer rounds. An engine that calculates to 1597 cc is sold as a 1.6; 1798 becomes an 1.8.

What is compression ratio?

The ratio of the full volume above the piston at the bottom of its travel to the chamber volume at the top. Higher means more efficient, and it means higher-octane fuel.

Oversquare or undersquare?

Oversquare means the bore exceeds the stroke: lower piston speed, higher safe revs, power at the top. Undersquare is the reverse — torque low down and a calmer character.

Worked example

A mass-market 1.6

Input: 82 mm bore, 75.6 mm stroke, four cylinders

Output: 1597 cc, which is 1.6 litres, ratio 1.08

Note: A ratio above one makes it oversquare, with peak power high in the range. With a 40 cc chamber the compression ratio comes out near 11, which already asks for decent fuel.

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Result

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