# Specific weight

The specific weight (also known as the unit weight) is the weight per unit volume of a material, or:

${\displaystyle \gamma =\rho \,g}$

where

${\displaystyle \gamma }$ is the specific weight of the material (weight per unit volume, typically N/m3 units)
${\displaystyle \rho }$ is the density of the material (mass per unit volume, typically kg/m3)
${\displaystyle g}$ is acceleration due to gravity (rate of change of velocity, given in m/s2)

Specific weight can be used in mechanical engineering to determine the weight of a structure designed to carry certain loads while remaining intact and remaining within limits regarding deformation. It is also used in fluid dynamics as a property of the fluid (e.g., the specific weight of water on Earth at 5°C is 9807 N·m−3 or 62.43 lbf·ft−3).

The terms specific gravity, and less often specific weight, are also used for relative density.