Engine Displacement Calculator (Bore & Stroke)
Calculate engine displacement from bore, stroke and cylinder count in mm or inches, solve for the bore or stroke a target size needs, and see bore/stroke ratio, overbore and stroker gains, piston speed and compression ratio.
How it works
Cylinder volume = (π ÷ 4) × bore² × stroke · Displacement = cylinder volume × cylinders · Bore = √(V ÷ (cylinders × π/4 × stroke)) · Stroke = V ÷ (cylinders × π/4 × bore²) · 1 cc = 1,000 mm³ · 1 cu in = 16.387 cc · Piston speed = 2 × stroke × rpm ÷ 60 · Compression ratio = (cylinder volume + clearance) ÷ clearance
Displacement is the volume all the pistons sweep in one full stroke. Each bore is a circle with area π ÷ 4 × bore², and the piston moves that circle a distance equal to the stroke, so one cylinder sweeps π ÷ 4 × bore² × stroke. Multiply by the number of cylinders for the engine size. Enter bore and stroke in millimeters, inches or centimeters; the result is shown in cc, liters and cubic inches. Switch "Solve for" to work backwards: give a target size and the stroke to get the bore you need, or the bore to get the stroke — handy when planning an overbore or a stroker crank. The bore/stroke ratio describes the engine's shape: over-square engines (ratio above 1) have room for bigger valves and rev more freely, while under-square, long-stroke engines tend to make more low-rpm torque. Under More options you can compare a rebuilt engine with a new bore and stroke, get the mean piston speed at a given rpm, the compression ratio from the clearance volume, and the specific output in hp per liter. A table lists the displacement after common overbores in both metric and inch sizes.
Worked example
With an 86 mm bore and 86 mm stroke, the piston area is 0.785398 × 86² = 5,808.8 mm², so one cylinder sweeps 5,808.8 × 86 = 499,557 mm³, or 499.6 cc. Four cylinders make 1,998 cc — about 2.0 L or 121.9 cubic inches — with a bore/stroke ratio of exactly 1 (a square engine). A classic small-block V8 with a 4.000 in bore and 3.480 in stroke works out to 0.785398 × 4² × 3.48 × 8 = 349.9 cubic inches (5,733 cc), the "350". Boring it 0.030 in over to 4.030 in adds about 5.3 cubic inches, to 355.1.
Sources: Engine displacement — Wikipedia · NIST — SI units of length and volume (1 in = 25.4 mm)
Frequently asked questions
What is the difference between bore and stroke?
Bore is the diameter of the cylinder; stroke is the distance the piston travels between top and bottom dead center, which equals twice the crankshaft throw. Bore sets the circular area swept and stroke sets how far it is swept; together with the cylinder count they define displacement.
How do I convert cc to liters or cubic inches?
Divide cc by 1,000 for liters, or by 16.387 for cubic inches. So 1,998 cc ≈ 2.0 L ≈ 122 cu in. Manufacturers round the badge figure, which is why a 1,998 cc engine is called a 2.0 and a 5,733 cc V8 a 350.
How much does an overbore add?
Displacement grows with the square of the bore, so a small overbore adds a few percent. On a 4.000 in bore, 0.030 in over adds about 1.5%; a 1 mm overbore on an 86 mm bore adds about 2.3%. The overbore table shows the common sizes for your engine, and the comparison option lets you enter any new bore and stroke.
How do I find the bore needed for a target size?
Choose Solve for: Bore, enter the target displacement (in cc, liters or cubic inches), the stroke and the number of cylinders. The calculator divides the target by the cylinder count and by π ÷ 4 × stroke and takes the square root. Solve for: Stroke works the same way when the bore is fixed, for example when picking a stroker crank.
What does the bore/stroke ratio tell me?
Above 1 is over-square (short stroke): bigger valves fit and the pistons travel less per revolution, so the engine can rev higher. Below 1 is under-square (long stroke), which favors low-rpm torque and a compact combustion chamber. Most modern car engines sit between about 0.85 and 1.2.
Does bigger displacement always mean more power?
No. Displacement sets how much air an engine can move per cycle, but turbocharging, higher rpm, better breathing and efficiency let small engines match larger ones. That is why the calculator can also show power per liter: a 2.0 L turbo making 300 hp produces 150 hp/L, far more than a typical naturally aspirated V8.
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Educational estimate — real-world figures vary with load, temperature, traction, tuning and measurement method.