What engine displacement measures
Displacement is the volume swept by the pistons between top and bottom dead center. For one cylinder, multiply its circular cross-sectional area by the stroke. The combustion chamber remaining above the piston at top dead center is excluded.
Bore and stroke formula
D is cylinder bore, S is stroke and N is cylinder count. With dimensions in millimeters, divide cubic millimeters by 1,000 to obtain cc, then divide cc by 1,000 for liters. One cubic inch equals 16.387064 cc; multiply a dimension in inches by 25.4 before entering it.
V = π × D² × S × N ÷ 4 ÷ 1000
Example: four cylinders with an 86 × 86 mm bore and stroke
The cylinder area is approximately 5,808.8 mm². An 86 mm stroke produces 499.56 cc per cylinder. Four identical cylinders give 1,998.23 cc, or 1.998 liters. This explains why an engine marketed as a 2.0-liter can have a slightly smaller exact displacement.
Using the calculator for a bore or stroke change
Use the finished bore after machining, rather than the original block specification. For a different crankshaft, use its actual stroke. Bore is squared: a 1% larger bore with unchanged stroke adds roughly 2.01% displacement. A 1% longer stroke adds 1% displacement.
What displacement cannot tell you
This calculation assumes identical cylinders in a conventional piston engine. It does not determine horsepower, durability, allowable wall thickness or compression ratio. Compression requires the clearance volume at top dead center. Use the vehicle documents when an official registered displacement is needed.