ENGINE TOOL

Compression Ratio Calculator

Estimate static compression ratio from swept volume and the volumes left above the piston at top dead center.

Engine dimensions

Cylinder bore (in)

Stroke (in)

Chamber volume (cc)

Piston volume (cc, dish + / dome -)

Head-gasket bore (in)

Compressed gasket thickness (in)

Deck clearance (in)

Results

Enter your numbers and calculate.

Compression-ratio formula

CR = (swept volume + clearance volume) ÷ clearance volume

Clearance volume includes the combustion chamber, piston dish or dome, head-gasket volume and deck-clearance volume. In this calculator, a piston dish is entered as a positive volume and a dome as a negative volume.

Static versus dynamic compression

Static compression ratio is purely geometric. Dynamic compression also considers when the intake valve closes, so camshaft timing can dramatically change the effective compression seen by the trapped charge.

Small measurement errors can noticeably change calculated compression ratio. Use measured chamber, piston, gasket and deck values when accuracy matters.