Engine Displacement Calculator
Quick answer: Engine displacement = π/4 × bore² × stroke × number of cylinders (bore and stroke in the same unit). For example, an 86 mm bore × 86 mm stroke × 4 cylinders gives 1,998.2 cc ≈ 2.0 liters ≈ 121.9 cubic inches.
Find out your engine's true size in cc, liters, and cubic inches. Enter the bore, stroke, and cylinder count in millimeters or inches, and this engine displacement calculator computes the total swept volume instantly.
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Estimate based on nominal bore and stroke; does not account for head gasket volume or combustion chamber.
How to use this calculator
Pick millimeters or inches for bore and stroke, then enter the cylinder bore (diameter), the stroke (piston travel), and the number of cylinders. The displacement is shown in cubic centimeters, liters, and cubic inches instantly.
How it works
Displacement = π/4 × bore² × stroke × cylinders. Each cylinder sweeps the area of the bore (a circle: π/4 × bore²) times the stroke distance, and the cylinders add together. Inputs in inches are converted to millimeters first using the exact definition 1 in = 25.4 mm, then results are shown in cc (cm³), liters (cc ÷ 1,000), and cubic inches (cc ÷ 16.387064).
Worked example
86 mm bore × 86 mm stroke × 4 cylinders: π/4 × 86² × 86 × 4 = 1,998,227.9 mm³ = 1,998.2 cc ≈ 2.0 liters ≈ 121.9 cu in.
Reference data
| Constant | Value | Status |
|---|---|---|
| 1 inch in millimeters | 25.4 mm | exact (defined) |
| 1 cubic inch in cubic centimeters | 16.387064 cm³ | exact (defined) |
| π (pi) | 3.141592653589793 | mathematical constant |
Source: National Institute of Standards and Technology (NIST) — SI unit definitions (exact, 2026).
Method & sources
Method: V = π/4 × bore² × stroke × cylinders; 1 cc = 1 cm³ = 1,000 mm³; liters = cc ÷ 1,000; cubic inches = cc ÷ 16.387064. Bore and stroke are user-entered; all conversion factors are exact definitions.
- Conversion constants — NIST SI definitions, nist.gov.
- Bore, stroke, cylinder count — user-entered.
Frequently asked questions
How is engine displacement calculated?
Displacement = π ÷ 4 × bore² × stroke × number of cylinders, with bore and stroke in the same unit. An 86 mm bore × 86 mm stroke × 4 cylinders gives 1,998.2 cc — about 2.0 liters.
What units should I enter bore and stroke in?
Either millimeters or inches — use the toggle above the calculator. Both bore and stroke must be in the same unit; the calculator converts internally (1 in = 25.4 mm exactly).
How do you convert cc to liters and cubic inches?
Divide cubic centimeters by 1,000 to get liters, and by 16.387064 to get cubic inches. For example, 1,998.2 cc ≈ 2.0 L ≈ 121.9 cu in.
Is displacement the same as engine size?
Essentially, yes: displacement is the total swept volume of all cylinders — the air-fuel mixture one complete engine cycle moves. A '2.0 L' engine sweeps about 2 liters per cycle.
Why is 25.4 mm per inch treated as exact?
Because it is defined exactly: the international yard and pound agreement defines 1 inch as exactly 25.4 mm, so 1 cubic inch is exactly 16.387064 cubic centimeters (per NIST).