The specific weight, , of a material is defined as the product of its density, , and the standard gravity, : 
The density of the material is defined as mass per unit volume, typically measured in kg/m. The standard gravity is acceleration due to gravity, usually given in m/s, and on Earth usually taken as .
Unlike density, specific weight is not a fixed property of a material. It depends on the value of the gravitational acceleration, which varies with location. Pressure may also affect values, depending upon the bulk modulus of the material, but generally, at moderate pressures, has a less significant effect than the other factors.