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The 'specific weight' (also known as the 'unit weight') is the weight per unit volume of a material, or:
:$gamma\; =$
ho , g
where
:$gamma$ is the specific weight [ML⁻²T⁻² or N·m⁻³]
:$$
ho is the density of the material [ML⁻³ or kg·m⁻³]
:$g$ is acceleration due to gravity at the Earth's surface [LT⁻² or m·s⁻²]
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 is 9807 Nm⁻³ at 5°C).
The terms ''specific gravity'', and less often ''specific weight'', are also used for relative density.