Engine Displacement Calculator (cc)

What displacement means

Displacement (also called engine capacity or swept volume) is the volume the pistons sweep as they move from the bottom to the top of their stroke, added up for all cylinders. It is the "1.6" in a 1.6-litre car or the "150" in a 150 cc scooter. It does not include the combustion chamber above the piston at top dead centre; that small extra volume matters for the compression ratio.

The formula

Each cylinder is a cylinder in the geometric sense, so its swept volume is the area of the bore times the stroke.

Volume per cylinder (cc) = π ÷ 4 × bore² × stroke ÷ 1000 (bore and stroke in mm)
Displacement = volume per cylinder × number of cylinders
Cubic inches = cc ÷ 16.387

Dividing by 1000 converts cubic millimetres to cubic centimetres (cc), which are the same as millilitres.

Worked examples

A four-cylinder car engine

Bore 86 mm, stroke 86 mm, 4 cylinders. One cylinder: 0.7854 × 86² × 86 ÷ 1000 = 499.6 cc. Four cylinders: 1,998 cc, sold as a 2.0-litre engine. In cubic inches that is 1,998 ÷ 16.387 = 121.9 ci.

A classic scooter bore-up

A classic 150 cc two-stroke scooter engine with a 57.8 mm bore and 57 mm stroke displaces 0.7854 × 57.8² × 57 ÷ 1000 = 149.6 cc. Fitting a 63 mm cylinder and piston on the same crankshaft gives 0.7854 × 63² × 57 ÷ 1000 = 177.7 cc, an increase of about 19%.

Bore versus stroke

• Square engine: bore equals stroke, as in the 86 × 86 mm example.
• Oversquare (short-stroke): bore larger than stroke. Room for bigger valves and higher revs; common in sports bikes.
• Undersquare (long-stroke): stroke longer than bore. Tends to give strong low-rpm torque; common in diesels and many economy engines.

Mean piston speed rises with stroke and rpm (mean piston speed = 2 × stroke × rpm ÷ 60), which is one reason long-stroke engines are usually limited to lower revs.

Bore-up and stroker kits

There are two ways to add capacity:

• Bore-up: a larger cylinder and piston. Because bore is squared in the formula, a small increase in bore adds a lot of capacity: going from 57.8 to 63 mm (+9% bore) adds about 19% volume.
• Stroker: a crankshaft with a longer throw. Capacity rises in direct proportion to the stroke.

Either change also raises the compression ratio unless the combustion chamber is enlarged, and usually needs matching changes to carburation or fuel injection, ignition and cooling. In many countries a change in engine capacity must also be declared for registration and insurance.

Rounding and marketing names

Manufacturers round displacement for model names, and tax bands are often based on the exact registered figure. A "1.6" engine may be anywhere from about 1,560 to 1,640 cc, and a "125" scooter is often 124.x cc to stay within licence rules.

Common mistakes

• Using radius instead of diameter. The formula uses bore (diameter) with π ÷ 4; if you use the radius, use π × r² instead.
• Mixing inches and millimetres. For bore and stroke in inches, multiply π ÷ 4 × bore² × stroke × cylinders to get cubic inches directly.
• Forgetting the cylinder count on multi-cylinder engines.

Typical engine sizes

Displacement is not the same as power

A bigger engine can burn more fuel and air per revolution, so it tends to make more torque, but power also depends on rpm, turbocharging, valve timing and efficiency. Many modern 1.0–1.5 litre turbocharged engines produce as much power as older naturally aspirated engines of 2.0 litres or more. Use the horsepower and torque calculator to see how torque and rpm combine into power.

Why capacity matters on paper

Engine capacity often appears in vehicle registration, road-tax bands, insurance groups and driving-licence categories (for example, learner and small-motorcycle categories based on cc or power). Always use the exact registered figure from your documents for these purposes, not a rounded marketing number.

Frequently asked questions

Sources

• Heywood JB. Internal Combustion Engine Fundamentals, 2nd ed. McGraw-Hill, 2018 (engine geometry and swept volume).
• NIST Handbook 44, Appendix C: 1 cubic inch = 16.387064 cm³.

Last reviewed 5 October 2026. Results are estimates; see our disclaimer.