How it works
Engine displacement is the total volume the pistons sweep. One cylinder sweeps V = (π/4) · bore² · stroke and the engine displacement is that times the number of cylinders. The bore/stroke ratio (bore ÷ stroke) describes the engine's character: oversquare (> 1) breathes well at high RPM, undersquare (< 1) makes low-end torque. Displacement is swept volume only — it does not set the compression ratio, which also depends on the combustion-chamber volume.
Worked example
An 86 mm bore × 86 mm stroke four-cylinder: each cylinder sweeps
(π/4) × 86² × 86 ≈ 500 cc, so the engine is about
1,998 cc — 2.0 litres, 122 ci. The bore/stroke ratio is 1.0, a
square engine. The calculator returns exactly this.
Frequently asked questions
- How do you calculate engine displacement from bore and stroke?
- Displacement = (π/4) × bore² × stroke × number of cylinders. The (π/4)·bore²·stroke part is the swept volume of one cylinder; multiply by the cylinder count for the total.
- How do I convert between cc, litres and cubic inches?
- 1,000 cc = 1 litre, and 1 cubic inch = 16.387 cc. The calculator shows all three at once.
- What is the bore/stroke ratio?
- Bore ÷ stroke. Above 1.0 is oversquare (bore wider than the stroke) — it favours high RPM; below 1.0 is undersquare (long stroke) — it favours low-end torque; 1.0 is square.
- Does displacement include the compression ratio?
- No. Displacement is only the swept volume. The compression ratio also depends on the combustion-chamber (clearance) volume, which this does not include.
- Can I use this for a hydraulic cylinder or pump?
- Yes — set cylinders to 1. The same (π/4)·bore²·stroke gives the swept (displaced) volume per stroke of a cylinder or pump.
- Does it work in metric and imperial?
- Yes — enter bore and stroke in mm or inches; displacement is shown in cc, litres and cubic inches.
Method & assumptions
- Displacement is swept volume only; the compression ratio additionally needs the combustion-chamber (clearance) volume.
- The same formula gives a hydraulic cylinder or pump's swept volume per stroke (use one cylinder).
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