Engine displacement calculator
Displacement from bore, stroke and cylinder count.
Fill in the fields and the result will appear here automatically.
A piston engine’s swept displacement follows from bore, stroke and the number of identical cylinders. The tool shows one cylinder’s volume, total cm³ and litres, and the stroke-to-bore ratio. That ratio describes geometry, not by itself torque or peak-power speed. A calculation from entered dimensions does not replace the manufacturer’s or documented displacement.
How it works
Formula and logic
V = π/4 · D² · S · n, with cubic millimetres divided by 1000. D and S are in mm, and n is a whole number from 1 to the largest safe integer. For one cylinder use n = 1; 1000 cm³ = 1 L. Zero dimensions, fractional cylinder counts and unrepresentable output volumes are rejected.
Example
Four cylinders of 82×86 mm give 1816.67 cm³ — the familiar "1.8 litres".
Fields and units
- Cylinder bore, mm — mm
- Piston stroke, mm — mm
- Cylinders — items
How to use
- — Bore and stroke in millimetres, as parts catalogues print them.
- — Boring the block changes the bore but not the stroke: enter the actual liner size.
- — A stroke-to-bore ratio above one means a long-stroke engine, below one a short-stroke.
- — This is the swept volume. The total combustion chamber volume is larger by the clearance volume.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- D and S are in mm, and n is a whole number from 1 to the largest safe integer. For one cylinder use n = 1; 1000 cm³ = 1 L.
FAQ
Why do the papers say something else?
A model name may use rounded displacement. A geometric calculation from bore and stroke helps compare cylinder dimensions and may differ from the documented value. Tax, registration or customs use requires the relevant documents and applicable rules; this calculator does not establish legally accepted displacement.
What does boring the block do?
Every extra millimetre of bore adds volume quadratically: on an 82 mm engine, boring to 83 adds about 45 cm³ across four cylinders. The stroke stays put — it is set by the crankshaft.
How does a long-stroke engine differ?
S/D above 1 describes a long-stroke geometry and below 1 a short-stroke one. The actual curve also depends on breathing, valve timing, boost and permitted engine speed; the ratio alone cannot establish low-speed torque.
Does this work for a motorcycle?
Yes, the formula does not care about the vehicle. For a single-cylinder engine enter one and the calculation shows the same volume in both rows.