Engine Displacement Calculator
Bore, stroke and cylinder count to cc, liters and cubic inches - plus the builder's numbers nobody bundles: bore/stroke character, rod ratio, mean piston speed, and what the common overbores buy you.
Enter Engine Measurements
Engine Geometry Results
| Measurement | Value |
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Mean piston speed in context
Common overbores
Rebuild pistons come in standard oversizes. Stroke stays the same, and displacement grows with the square of the bore.
| Overbore | New bore | Cubic inches | cc |
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How displacement is calculated
One cylinder's swept volume is the circle of the bore times the stroke: pi/4 x bore squared x stroke. Multiply by the cylinder count for total displacement. The unit bridge is exact, not rounded: one inch is exactly 25.4 mm, so one cubic inch is exactly 16.387064 cc - which is why a 350 cubic inch small block is 5,733 cc, and why marketing rounds it to 5.7 liters. Displacement feeds directly into the compression ratio calculator, which uses the same bore and stroke inputs in the same units, into carb sizing via the carb CFM calculator, and into fuel sizing via the injector size calculator. The overbore table covers the machining half of a rebuild; the other lever is the crank - put a 3.750 in stroker crank in a +0.030 350 and you get the classic 383 (382.7 ci - type it in and check).
Oversquare, square, undersquare
The bore/stroke ratio describes the shape of the cylinder, and shape is destiny. An oversquare engine (bore larger than stroke) has room for bigger valves and, for the same piston speed, can turn more rpm - the classic recipe for a power-happy engine. An undersquare engine trades that for a longer lever on the crank and a smaller bore that helps combustion at low rpm, which is why long-stroke engines tend toward low-end torque and early peaks. Neither is better; they are tuned for different jobs, and the drawing above shows your engine's shape to scale.
Rod ratio and mean piston speed
Rod ratio (rod length divided by stroke) does not change displacement at all - it changes how the piston moves. A low ratio increases rod angularity and piston side-load; most production engines land between 1.5 and 1.8, and builders often call 1.75 to 1.8 ideal. Mean piston speed - two strokes per revolution, so 2 x stroke x rpm - is the classic back-of-envelope limit on engine speed, because it is what the rings, the piston skirt, and the oil film actually experience. Published typical values: around 16 m/s for an ordinary street car at redline, 20 to 25 m/s for sport engines, about 25 m/s for NASCAR and Formula One, and about 30 m/s for Top Fuel and MotoGP. These are descriptions of existing engines, not permission slips - what your rotating assembly tolerates depends on what it is made of.