Engine displacement calculator: cc, litres and cubic inches
This engine displacement calculator works out an engine’s capacity from its bore, stroke and number of cylinders, in cubic centimetres (cc), litres and cubic inches. Enter the measurements in millimetres or inches; switching units converts the boxes for you.
It is also a compression ratio calculator. Add the combustion chamber volume, head gasket size, piston-to-deck height and piston dish or dome, and it gives the static compression ratio, with each part of the clearance volume listed. With the rod length and intake valve closing angle it adds the dynamic compression ratio, and with engine speed the mean piston speed. Engine builders can use it while choosing pistons, gaskets or a skim; students can use it to check homework.
How to calculate engine displacement and compression ratio
- Choose Millimetres or Inches.
- Enter the Bore, Stroke and number of Cylinders; the displacement appears straight away.
- For compression, enter the Combustion chamber volume, the Gasket bore and compressed Gasket thickness, the Piston to deck distance and the Piston dish or dome.
- Optionally add the Rod length, the cam’s Intake valve closes angle and an Engine speed.
- Read the results and the per-cylinder volume table, or copy them.
Engine Displacement & Compression Ratio Calculator features
Three units at once
cc, litres and cubic inches, using the exact 1 inch = 25.4 mm.
Full clearance volume
Chamber, gasket, deck height and dish or dome, with signs handled for pop-up pistons.
Dynamic compression
From exact crank-and-rod geometry at the intake closing point.
Bore/stroke and piston speed
Square, oversquare or undersquare, and mean piston speed in m/s.
Unit switch converts values
Change mm to inches without retyping.
Engine displacement formula
Displacement = π ÷ 4 × bore² × stroke × number of cylinders. With millimetres, divide by 1,000 for cc; with inches the answer is in cubic inches, and 1 cubic inch = 16.387064 cc, so litres = cubic inches × 0.016387.
Worked example: a four-cylinder engine with an 86 mm bore and 86 mm stroke sweeps 0.7854 × 86² × 86 = 499,558 mm³ per cylinder, or 499.6 cc; four cylinders make 1,998.2 cc — sold as a “2.0 litre”. A V8 with a 4.00 in bore and 3.48 in stroke gives 0.7854 × 16 × 3.48 × 8 = 349.85 cubic inches, about 5.7 litres: the “350”.
Compression ratio formula
Static compression ratio = (swept volume + clearance volume) ÷ clearance volume, for one cylinder. The clearance volume is everything above the piston at top dead centre: the chamber in the head, the gasket hole (π ÷ 4 × gasket bore² × thickness), the gap between piston and deck (π ÷ 4 × bore² × distance) and the piston’s dish or valve reliefs. A dome reduces it, and so does a piston that rises above the deck.
In the example, a 45 cc chamber, 0.8 mm gasket with an 88 mm hole (4.87 cc), 0.2 mm deck (1.16 cc) and 6 cc dish give 57.03 cc of clearance, so the ratio is (499.56 + 57.03) ÷ 57.03 = 9.76 : 1. A thinner gasket or a skimmed head shrinks the clearance and raises the ratio.
Static vs dynamic compression
The intake valve closes after bottom dead centre, so the piston only starts compressing part-way up the bore. The dynamic ratio uses the piston’s distance from top dead centre at that point: x = r(1 − cos θ) + l − √(l² − r² sin² θ), with r half the stroke, l the rod length and θ = 180° + the closing angle. Cam cards quote closing angles at different lifts (advertised or at 0.050 in), and the result changes with that choice — compare like with like.
Displacement tells you size, not power: for a power estimate use the cc to hp calculator, and for twisting force the torque calculator.
Engine Displacement & Compression Ratio Calculator FAQ
How do you calculate engine displacement in cc?
Multiply π ÷ 4 by the bore squared, the stroke and the number of cylinders, using millimetres, then divide by 1,000. The engine displacement calculator above does this and also shows litres and cubic inches.
How do I convert cubic inches to litres?
Multiply by 0.016387064 (1 cubic inch is exactly 16.387064 cc). 350 cubic inches is 5.74 litres.
How do you calculate compression ratio?
Add up the clearance volume above the piston at TDC — chamber, gasket, deck and dish or dome — then divide (swept volume + clearance volume) by the clearance volume.
Does a thinner head gasket raise compression?
Yes. A thinner gasket reduces the gasket volume; in the example, going from 0.8 mm to 0.5 mm removes about 1.8 cc and raises the ratio from 9.76 to about 10.05 : 1.
What is a good dynamic compression ratio?
It depends on fuel octane, combustion chamber design and cooling, so there is no single safe figure. Follow the engine or cam maker’s guidance.
Why is my car’s official cc slightly different?
Makers round, and the bore and stroke they publish are themselves rounded. Small differences of a few cc are normal.