Engine Compression Ratio Calculator

Linear Unit (bore, stroke, gasket…)

All linear inputs use this unit.

Volume Unit (chamber, piston…)

All volume inputs use this unit.

Cylinder Bore

Internal diameter of the cylinder. Typical: 70–105 mm.

Piston Stroke

Distance piston travels from BDC to TDC. Typical: 65–105 mm.

Number of Cylinders

3, 4, 6, 8, 10, 12 — used for total displacement.

Deck Clearance

+ piston below deck · − piston above deck. Typical: 0.3–1.5 mm.

Combustion Chamber Volume

Volume of the head combustion chamber. Typical: 35–75 cc.

Piston Dome / Dish Volume

+ dome (raises CR) · − dish (lowers CR) · 0 flat-top.

Head Gasket Bore

Inner diameter of the head gasket opening. Usually bore + 1–3 mm.

Head Gasket Compressed Thickness

Compressed (fire-ring) thickness. Typical: 0.8–2.0 mm.