Engine Displacement Calculator: Bore, Stroke and Cylinders

1. Pick the unit your spec sheet uses, millimetres or inches. Most modern engines list millimetres; classic American V8s list inches.
2. Enter the bore (the cylinder diameter) and the stroke (how far the piston travels). These are usually printed together as "bore x stroke".
3. Enter the number of cylinders, then read the displacement in cc, litres and cubic inches. The answer updates as you type.

In this guide cc means cubic centimetres, L means litres and cu in means cubic inches. The tool shows all three at once.

Engine displacement is the total volume that all the pistons sweep in one full cycle. Each piston moves down its cylinder, and the volume it uncovers is that cylinder swept volume. Add every cylinder together and you have the engine displacement.

It is the single number used to describe engine size. A "2.0 litre" engine has cylinders that sweep about 2000 cubic centimetres between them. A "350" small-block sweeps about 350 cubic inches. The same engine can be quoted either way, because cc, litres and cubic inches are just different units for the same volume.

Displacement matters because it sets how much air and fuel an engine can draw on each cycle, which strongly influences power, torque and fuel use. It is also used for tax bands, racing classes and insurance in many countries.

One caution: displacement is swept volume only. It does not include the combustion chamber above the piston at the top of its travel, so it is not the same as the total cylinder volume used in a volume calculator or in a compression-ratio figure. For the acceleration a given engine delivers, see our 0-60 mph acceleration calculator.

Each cylinder is a circle swept along the stroke, so its volume is the area of the bore circle times the stroke length. The area of a circle of diameter d is (pi/4) times d squared, which gives the compact form below.

1. Convert bore and stroke to centimetres. Millimetres divide by 10; inches multiply by 2.54. Example: 86 mm = 8.6 cm.
2. Find one cylinder: (pi/4) x 8.6 x 8.6 x 8.6 = 499.56 cc.
3. Multiply by the cylinder count: 499.56 x 4 = 1998 cc, which is 2.0 litres.

To change units, divide cc by 1000 for litres, and divide cc by 16.387064 for cubic inches. That factor is exact because one inch is defined as exactly 2.54 centimetres, so one cubic inch is 2.54 cubed, or 16.387064, cubic centimetres.

The math is pure geometry and carries no rounding error of its own. The only judgement is how many decimals you show. Engineers quote cc to the nearest whole number and litres to one decimal place.

A square 2.0 litre four-cylinder. With a bore of 86 mm and a stroke of 86 mm, one cylinder is (pi/4) x 8.6 x 8.6 x 8.6 = 499.56 cc. Four of them give 1998 cc, rounded to 2.0 L or about 122 cubic inches. The bore equals the stroke, so the ratio is 1.00 and the engine is "square".

The classic Chevrolet 350 V8. With a bore of 4.00 in and a stroke of 3.48 in, convert to 10.16 cm and 8.84 cm. One cylinder is about 716.6 cc, and eight cylinders give about 5733 cc, or 5.7 L, or about 350 cubic inches. That is where the "350" name comes from. The bore is wider than the stroke, so it is oversquare.

A small three-cylinder. A 71.9 mm bore and 82.0 mm stroke across three cylinders gives roughly 999 cc, the "1.0 litre" turbo triples common in small cars. The long stroke makes it undersquare, favouring low-rpm torque.

Notice that two engines can share a displacement yet feel very different, because bore and stroke, not just total volume, shape how they breathe and rev.

Displacement tells you the size of an engine, but the bore-to-stroke ratio tells you a lot about its personality. The ratio is simply the bore divided by the stroke.

A wider bore leaves room for bigger valves and shortens the distance the piston travels, so the engine can spin faster safely. A longer stroke gives the crankshaft more leverage, which helps low-speed torque but limits revs. Two engines of the same displacement can therefore behave very differently.

The formula is fixed, but a few things decide the number you get and how to read it.

Bore and Stroke Together

Displacement rises with the square of the bore but only in proportion to the stroke, so widening the bore adds volume faster than lengthening the stroke by the same amount.

Cylinder Count

Doubling the cylinders doubles the displacement for the same bore and stroke. A 500 cc single and a 2000 cc four can share the same cylinder size.

Measured Versus Nominal

Makers round the headline figure. A "2.0 litre" may really be 1984 or 1998 cc. Use the true bore and stroke for the exact number.

What Displacement Does Not Tell You

It says nothing about forced induction. A small turbo engine can out-power a larger naturally aspirated one, which is why displacement alone no longer predicts output. It also ignores fuel economy, which depends on load and gearing; for that, see a gas mileage calculator.

Checking a Rebuild or a Bore Job

Overboring a cylinder raises displacement. Enter the new bore to see the new size before you commit to machining.

Converting Between Cc, Litres and Cubic Inches

A spec sheet in one unit and a part listed in another are easy to line up once you have all three figures.

Comparing Engines

Put two engines side by side by displacement and by bore-to-stroke ratio to understand why they feel different.

Tax, Class and Insurance Bands

Many countries band vehicles by engine size. Confirm which band an engine falls into before a purchase or an import.

Learning the Geometry

The formula is a clean, real-world use of the cylinder-volume equation, useful for students and new mechanics alike.

1. Forgetting to Multiply by the Cylinder Count

(pi/4) x bore squared x stroke gives one cylinder, not the whole engine. Multiply by the number of cylinders.

2. Mixing Units

Bore in millimetres and stroke in inches gives nonsense. Convert both to the same unit first; this tool does it for you.

3. Using Radius Instead of Diameter

Bore is the full diameter of the cylinder, not the radius. The (pi/4) form already uses the diameter.

4. Confusing Displacement with Compression

Displacement is swept volume only. It excludes the combustion chamber, so it is not the number used for compression ratio.

5. Trusting the Rounded Badge

A "5.0" or "350" badge is rounded. For anything precise, calculate from the real bore and stroke.

The geometry is exact. The only judgement is how many decimals to display and how precisely you know the bore and stroke.

Find one cylinder with (pi/4) times bore squared times stroke, using centimetres, then multiply by the number of cylinders. An 86 mm by 86 mm four-cylinder gives 1998 cc, or 2.0 litres.

2.0 litres is 2000 cc, and 2000 divided by 16.387064 is about 122 cubic inches. A real 86 by 86 mm four is 1998 cc, which rounds to 2.0 litres.

Its 4.00 inch bore and 3.48 inch stroke across eight cylinders give about 350 cubic inches, or roughly 5733 cc, which rounds to 5.7 litres. The badge is the cubic-inch figure.

Divide the cc figure by 16.387064. That factor is exact because one inch is exactly 2.54 centimetres, so one cubic inch is 2.54 cubed cubic centimetres.

Bore is the diameter of the cylinder. Stroke is how far the piston travels. Together they set the swept volume and the engine character.

Oversquare means the bore is wider than the stroke, which suits high revs. Undersquare, or long-stroke, means the stroke is longer, which favours low-rpm torque. Square means they are equal.

No. Displacement is swept volume only. Compression ratio compares the full cylinder volume at the bottom to the small volume at the top, including the combustion chamber.

Not any more. A small turbocharged engine can beat a larger naturally aspirated one. Displacement sets the air an engine draws unforced, but boost and tuning change the outcome.

Use the full bore diameter. The (pi/4) form of the formula already accounts for turning that diameter into a circle area, so there is no need to halve it.

No. The math runs in your browser. Anything you Save stays in your own browser storage until you clear it.

• NIST guide to the SI, conversion factors for length and volume (exact inch = 2.54 cm) (NIST SP 811, Appendix B.9).
• Engine displacement: swept volume, formula and units (engineering reference overview).
• Stroke ratio: oversquare, square and undersquare engines (bore-to-stroke ratio definitions).
• Bore: cylinder diameter and its role in displacement (definition of engine bore).