Engine Displacement Calculator

Calculate total swept engine volume from bore, stroke, and cylinder count. See the result in cubic centimeters, liters, and cubic inches. Inputs stay in this browser tab.

For conventional reciprocating piston engines This tool assumes equal circular cylinders with the same bore and stroke. It does not model rotary engines, tapered or non-circular bores, or separate cylinder banks with different dimensions.

Engine dimensions

Changing units converts the current bore and stroke values.

Inside diameter of one cylinder.

Travel from TDC to BDC.

Whole numbers from 1 to 24.

Privacy: measurements are calculated locally. They are not uploaded, stored, or included in analytics events.

Calculated displacement

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Engine displacement formula

A cylinder's swept volume is the area of its circular bore multiplied by the piston stroke. Multiply that value by the number of equal cylinders:

total displacement = (π ÷ 4) × bore² × stroke × cylinders

When bore and stroke are in millimeters, the formula returns cubic millimeters; divide by 1,000 for cubic centimeters. When they are in inches, it returns cubic inches. This calculator uses the exact relationship 1 in³ = 16.387064 cm³ for the other display units.

What the number represents: displacement is swept volume only—the volume moved by the pistons between top dead center (TDC) and bottom dead center (BDC). It excludes clearance volume remaining above a piston at TDC.

How to measure and calculate engine size

  1. Use finished dimensions. Enter the actual finished bore after honing or overboring and the crankshaft's effective stroke.
  2. Keep units together. Bore and stroke must use the same unit. Select millimeters or inches before entering both values.
  3. Count equal cylinders. Enter the total number of cylinders sharing those dimensions. Calculate unequal banks or cylinders separately and add their volumes.
  4. Retain appropriate precision. The calculator preserves the mathematical result, but a published engine size may be rounded or classified under a specific regulatory convention.

Bore-to-stroke ratio

The result also reports bore ÷ stroke. A ratio above 1 means the bore is wider than the stroke is long, often called oversquare. A ratio below 1 is commonly called undersquare, and equal dimensions are square.

These labels describe geometry only. Displacement by itself does not determine power, torque, fuel economy, durability, emissions, or safe operating speed; those depend on the complete engine design and calibration.

Engine displacement FAQs

What is the engine displacement formula?

For equal circular cylinders, total displacement is (π ÷ 4) × bore² × stroke × cylinder count. Use the same length unit for bore and stroke.

Are engine displacement and engine size the same?

In everyday automotive use, engine size usually means swept displacement, stated in cc, liters, or cubic inches. It does not mean the engine's external physical dimensions.

Does displacement include the combustion chamber?

No. Swept displacement includes only the volume a piston displaces during its stroke. The clearance volume above the piston at TDC is part of a compression-ratio calculation, not engine displacement.

How do I calculate displacement after an overbore?

Enter the finished bore after machining. Keep the original stroke if the crankshaft geometry is unchanged, or enter the new stroke for a stroker crank. Then use the total cylinder count.

Why does a marketed engine size differ slightly?

Manufacturers and regulations may round or truncate a calculated swept volume, and nominal bore and stroke specifications may be published with limited precision. Use design or measured dimensions appropriate to your purpose.

Can this calculate rotary-engine displacement?

No. Rotary engines use changing chamber volume and a different convention. This calculator is for conventional reciprocating engines with circular cylinder bores.

Are my engine measurements tracked?

No. The calculation runs locally in your browser. This tool does not upload, store, or attach the values to analytics events.

Limits and engineering disclaimer

  • The calculation assumes every cylinder has a constant circular bore and identical stroke. Add separately calculated volumes for unequal cylinders.
  • Entered measurements, manufacturing tolerances, wear, surface finish, and rounding can make a measured result differ from a nominal or certified displacement.
  • The result does not determine piston-to-wall clearance, compression ratio, component compatibility, machining limits, or safe engine operation.

Engineering disclaimer: This is an educational geometry calculator, not a machining specification or engine-build approval. Use manufacturer data and qualified measurement or machining advice for component selection and safety-critical work.

Methodology and sources

Last reviewed: July 31, 2026. The swept-volume definition and unit conversion were checked against primary U.S. government references:

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