# Poisson's Ratio

## Description

Poisson’s ratio, named after Siméon Poisson, is the negative ratio of transverse to axial strain. When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called the Poisson effect. Poisson’s ratio (nu) is a measure of this effect. The Poisson ratio is the fraction (or percent) of expansion divided by the fraction (or percent) of compression, for small values of these changes.

Related formulas## Variables

ν | Poisson's ratio (dimensionless) |

δϵ_{z} | transverse strain (negative for axial tension (stretching), positive for axial compression) (pascal) |

δϵ_{x} | axial strain (positive for axial tension, negative for axial compression) (pascal) |