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Engine Displacement Calculator

Calculators · Added

Displacement is the volume every piston sweeps in one full stroke. The formula is short and has one trap in it — the bore is a diameter, not a radius — which is why getting it wrong puts the answer out by a factor of four rather than a little.

Bore and stroke are in

Cylinder diameter, not radius

Adds the compression ratio. Leave blank to skip it.

Try:

How to use the engine displacement calculator

  1. 1Enter the bore and stroke in millimetres or inches, and the number of cylinders.
  2. 2Read the displacement in cc, litres and cubic inches.
  3. 3Check the bore/stroke ratio, which says more about how the engine behaves than the capacity does.
  4. 4Add the combustion chamber volume if you want the compression ratio as well.

Examples

A Honda B16A

Input
81 × 77.4 mm, 4 cylinders
Result
1,595 cc — 1.6 litres — 97.3 cubic inches, and oversquare at 1.047

An American V8

Input
4.00 × 3.48 in, 8 cylinders
Result
5,735 cc — 350 cubic inches, which is where the name comes from

About the engine displacement calculator

Why capacity predicts less than it used to

Displacement sets how much air an engine can move per two revolutions, and for a naturally aspirated engine that is a hard ceiling on power. Forced induction removes the ceiling: a turbocharger pushes more air into the same volume, so a 2-litre turbo engine can outperform a 3-litre naturally aspirated one on both power and fuel consumption.

That is why capacity-based taxation and insurance classes have drifted out of step with performance, and why a modern badge is a poor guide to what is under the bonnet.

Getting capacity from a block

An engine builder cannot change much: the block fixes the bore within the limits of how much material can be removed, and the crankshaft fixes the stroke. Capacity is therefore bought either by boring out — a limited amount, and each pass thins the cylinder wall — or by fitting a longer-stroke crank, which is the larger change and the one that alters the engine's character as well as its size.

This is why the two reverse calculations matter as much as the forward one: the practical question is usually not what capacity a given bore and stroke give, but what stroke would reach a target capacity at the bore the block already has.

Frequently asked questions

What is the π over 4 for?
A cylinder's cross-section is πr², and the bore is given as a diameter. Substituting d/2 for r turns πr² into πd²/4, which is where the quarter comes from. Squaring the diameter without it overstates every cylinder by exactly four times, and it is the most common way this calculation is got wrong.
Does displacement include the combustion chamber?
No. Displacement is swept volume — what the piston moves through between bottom and top dead centre — and it stops at the top of the stroke. The space still above the piston at that point is the clearance volume, and it is what turns displacement into the compression ratio: (swept + clearance) ÷ clearance.
What does the bore/stroke ratio tell me?
Which way the engine leans. Oversquare, with the bore wider than the stroke, keeps piston speed lower at a given engine speed and leaves room for bigger valves, so it revs higher — typical of petrol sports engines and motorcycles. Undersquare gives the crank more leverage and more torque lower down at a lower rev ceiling, which is typical of diesels. It is a tendency rather than a rule: valve timing, induction and turbocharging move an engine's character much further than its proportions do.
Why does my figure not match the badge?
Because manufacturers round, and almost always upward. 1,998 cc is sold as a 2.0 and 1,595 cc as a 1.6. Marketing names diverge further still — plenty of badges have not matched the actual capacity since the 1990s, particularly on turbocharged engines where the number now suggests a power class rather than a volume.

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