Huber's equation, first derived by a Polish engineer Tytus Maksymilian Huber, is a basic formula in elastic material tension calculations, an equivalent of the equation of state, but applying to solids. In most simple expression and commonly in use it looks like this:^[1]

${\displaystyle \sigma _{red}={\sqrt {({\sigma }^{2})+3({\tau }^{2})}}}$

where ${\displaystyle \sigma }$ is the tensile stress, and ${\displaystyle \tau }$ is the shear stress, measured in newtons per square meter (N/m², also called pascals, Pa), while ${\displaystyle \sigma _{red}}$—called a reduced tension—is the resultant tension of the material.

Finds application in calculating the span width of the bridges, their beam cross-sections, etc.^{[citation needed]}