Engine Displacement Calculator

Calculate cubic inches and liters from bore, stroke, and cylinder count.

Displacement = π ÷ 4 × bore² × stroke × cylinder count. Changing units converts the current measurements.

How to calculate cubic inches and liters

  1. Select inches or millimeters for the measurements.
  2. Enter the cylinder bore: the inside diameter of one cylinder.
  3. Enter crankshaft stroke: the distance the piston travels between its highest and lowest positions.
  4. Enter the cylinder count. Eight is the starting value, but the tool also handles four-, six- and other cylinder counts.
  5. Read displacement in cubic inches (CID) and liters. Changing the unit selector converts the current bore and stroke values.

Engine displacement formula

Displacement = (π ÷ 4) × bore² × stroke × cylinder count

With bore and stroke in inches, the answer is cubic inches. Multiply CID by 0.016387064 to convert to liters. With measurements in millimeters, the same cylinder-volume formula gives cubic millimeters; divide by 1,000,000 for liters. The calculator converts millimeter inputs before doing its CID calculation.

Example: a 4.000-inch bore and 3.480-inch stroke

For eight cylinders, these dimensions calculate to 349.8 cubic inches, or approximately 5.733 liters. If the bore increases to 4.030 inches while stroke stays the same, displacement becomes approximately 355.1 cubic inches, or 5.819 liters.

This shows why an engine's familiar advertised size may differ from its calculated displacement. The actual bore and stroke, including any overbore or stroker crankshaft, determine the result.

Measuring a rebuilt engine

Use the finished cylinder bore rather than assuming the original factory dimension. An overbore specification is normally a change in diameter: adding a 0.030-inch overbore to a 4.000-inch bore gives 4.030 inches. Use the crankshaft's actual stroke. This calculator assumes all cylinders have the same bore and stroke.

Engine size questions

Does this work for flathead engines?

Yes. A conventional flathead uses the same swept-cylinder-volume formula as an overhead-valve engine. Enter the dimensions and cylinder count for your particular engine.

Is displacement the same as combustion chamber volume?

No. Displacement is the volume swept by the pistons. Combustion chamber and clearance volumes are separate inputs needed for a compression-ratio calculation.

Can I work out horsepower from cubic inches alone?

No. Displacement does not establish airflow, compression, cam timing, engine speed or efficiency. Use measured or otherwise justified horsepower in the quarter-mile calculator.

Why are cubic inches and liters both displayed?

They describe the same engine volume in different units. CID is convenient for traditional American engine combinations; liters make comparison with metric specifications easier.

Related calculators and workshop references

Return to all automotive calculators, check original specifications in the automotive manual library, or browse hot rod parts and workshop tools.