# Compression Ratio

on . Posted in Fluid Dynamics

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 Tags: Engine Equations