# Cubic Inch Displacement

on . Posted in Fluid Dynamics

Cubic inch displacement, abbreviated as CID, is the size of the engine.  It is a unit of measurement used to describe the volume of the combustion chamber in an internal combustion engine.  It is defined as the total volume swept by all the pistons in the engine over the entire length of their stroke.  The volume of each cylinder in an engine is calculated by measuring the diameter of the cylinder bore (the inside diameter of the cylinder) and multiplying it by the length of the stroke (the distance the piston travels in the cylinder).  The volume of all the cylinders is then added together to get the total cubic inch displacement of the engine.

## Cubic Inch Displacement formula

$$\large{ CID = NOC \; 0.7854 \; BORE^2 \; STROKE }$$
Symbol English Metric
$$\large{ CID }$$ = cubic inch displacement $$\large{in^3}$$ $$\large{mm^3}$$
$$\large{ NOC }$$ = number of cylinders $$\large{dimensionless}$$
$$\large{ BORE }$$ = cylinder bore size $$\large{in}$$ $$\large{mm}$$
$$\large{ STROKE }$$ = piston stroke length $$\large{in}$$ $$\large{mm}$$