Compression Ratio

The compression ratio, abbreviated as CR, a dimensionless number, in an engine is the ratio of the maximum volume to the minimum volume in a cylinder.  The equation and calculator below can help find the compression ratio. 

 

compression ratio formula
\(\large{ CR = 1 +  \frac{\pi}{4} \; \frac { BORE^2 \; STROKE }{CCV \;+\; HGV \;+\; PVD  }  }\)
Symbol	English	Metric
\(\large{ CR }\) = compression ratio	\(\large{dimensionless}\)
\(\large{ BORE }\) = bore	\(\large{in^2}\)	\(\large{mm^2}\)
\(\large{ CCV }\) = combustion chamber volume	\(\large{in^3}\)	\(\large{mm^3}\)
\(\large{ HGV }\) = head gasket volume	\(\large{in^3}\)	\(\large{mm^3}\)
\(\large{ \pi }\) = Pi	\(\large{3.141 592 653 ...}\)
\(\large{ PDV }\) = piston deck volume	\(\large{in^3}\)	\(\large{mm^3}\)
\(\large{ STROKE }\) = stroke length	\(\large{in}\)	\(\large{mm}\)

 

compression ratio formula
\(\large{ CR = \frac{ V_d \;+\; V_c }{ V_c }  }\)
Symbol	English	Metric
\(\large{ CR }\) = compression ratio	\(\large{dimensionless}\)
\(\large{ V_c }\) = clearance volume	\(\large{in^3}\)	\(\large{mm^3}\)
\(\large{ V_d }\) = displacement volume	\(\large{in^3}\)	\(\large{mm^3}\)

 

compression ratio calculator