Hello there,

In Mechanics and Material Science, Poisson's ratio is a measure of the Poisson effect, the deformation of a material in directions perpendicular to the direction of loading.

Poission's Ratio = - Transverse strain / Axial strain

Most materials have Poisson's ratio values ranging between 0.0 and 0.5. A perfectly rigid body has Poission's Ratio value equal to 0.

Hope this helps.