Engine Displacement Calculator
Find engine size from bore, stroke, and cylinders.
Results update as you type.
How it works
Engine displacement, the combined volume swept by all the pistons, is the single number most often used to describe an engine's size, and this engine displacement calculator derives it from the fundamental dimensions of bore, stroke, and cylinder count. Enter the bore and stroke in millimetres and the number of cylinders, and the tool returns displacement in both cubic centimetres and litres. Displacement matters because it broadly shapes an engine's character. A larger swept volume generally moves more air and fuel per cycle, which tends to raise torque and power potential, and it also feeds into tax brackets, insurance classes, and racing categories in many countries. Knowing how bore and stroke combine to produce that volume helps you understand why two engines of the same displacement can feel very different: a wide bore with a short stroke revs freely, while a narrow bore with a long stroke favours low-end torque. The calculation treats each cylinder as a simple cylinder in the geometric sense. The circular bore gives a cross-sectional area, the stroke gives the height the piston sweeps, and multiplying the two yields the volume of one cylinder. Scaling by the cylinder count totals the engine. Mechanics rebuilding a motor, enthusiasts comparing specifications, and students of engineering can all use this tool to move from raw measurements to the familiar displacement figure quickly and accurately.
displacement = (π ÷ 4) × bore² × stroke × cylinders
An engine's displacement is the total volume its pistons sweep in one cycle. Each cylinder is a circular bore, so its swept volume is the area of that circle, π divided by four times the bore squared, multiplied by the stroke length the piston travels. Converting bore and stroke from millimetres to centimetres gives the volume in cubic centimetres. Multiplying by the number of cylinders totals the whole engine, and dividing by 1,000 expresses it in litres.
Source:Standard engine displacement geometry
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter bore, stroke and number of cylinders.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Displacement updates instantly as you type — no button to press.
Frequently asked questions
What are bore and stroke?
Bore is the diameter of each cylinder, the circular hole the piston moves within, while stroke is the distance the piston travels from the bottom to the top of that cylinder. Together they define the swept volume of one cylinder. Both are usually given in millimetres on an engine's specification sheet, and both are needed alongside the cylinder count to calculate total displacement accurately.
How do I convert displacement to litres?
Displacement in litres is simply the cubic-centimetre figure divided by 1,000, since one litre equals 1,000 cubic centimetres. So a 1,998 cc engine is about 2.0 litres. Manufacturers usually round to one decimal place for marketing, which is why a 1,998 cc or 2,499 cc engine is sold as a 2.0 or 2.5 litre. This calculator shows both figures so you can see the exact volume.
What is the difference between an oversquare and undersquare engine?
An oversquare engine has a bore larger than its stroke, which lets it rev higher and typically favours peak power, common in sports and racing engines. An undersquare or long-stroke engine has a stroke larger than its bore, tending to produce strong low-end torque at lower RPM, common in trucks and older designs. A square engine has bore equal to stroke, balancing the two characteristics.
Does larger displacement always mean more power?
Not always. Displacement sets the potential air and fuel an engine can process, so all else equal a bigger engine makes more power. But forced induction, higher RPM limits, better breathing, and modern tuning let small engines match or beat larger ones. A turbocharged 2.0 litre can out-power a naturally aspirated 3.0 litre. Displacement is one important factor among several that determine an engine's output.
Why is displacement used for tax and racing classes?
Displacement is a stable, easily verified measure of engine size that correlates broadly with power and fuel use, which makes it a convenient basis for regulation. Many countries set vehicle tax bands and insurance groups by engine litres, and motorsport organisers define classes by displacement limits to keep competition fair. Because it is fixed by the engine's geometry, it cannot be quietly changed the way a tune can, making it reliable for rule-making.