What is the specific weight?
We explain what the specific weight is and what are the formulas it uses. In addition, some examples and their relationship with density.
What is the specific weight and its formula?
Specific gravity is the relationship between the weight and volume of a substance . Since the weight of an object is the extent to which the attraction of the Earth acts on it, and at the same time the volume is the surface that said object occupies, the specific weight constitutes the relationship between both properties expressed in Newtons per cubic meter (N / m ^{3} ), according to the International System.
The calculation of it, requires numerous other properties of the substance, such as density, mass and ordinary weight of the substance. This according to the following calculation formula, in which the specific weight is represented by the symbol gamma (γ) :
γ (specific weight) = w (ordinary weight) / V (volume of the substance), or what is the same: γ = w / V = mg / V, where m is the mass of the substance and g is the acceleration of gravity (commonly considered as 9.8 m / s ^{2} ). From there it is concluded that: γ = pg, where p is the density of the substance.
According to the International Bureau of Weights and Measures (BIPM), however, this term is not acceptable, “weight density” should be used instead.

Examples of specific weight
Some examples of different materials are:
 Plaster: 1250 N / m ^{3}
 Cal: 1000 N / m ^{3}
 Dry sand: 1600 N / m ^{3}
 Wet sand: 1800 N / m ^{3}
 Loose cement: 1400 N / m ^{3}
 Concrete slabs: 2200 N / m ^{3}
 Poplar wood: 500 N / m ^{3}
 Ash Wood: 650 N / m ^{3}
 American pine wood: 800 N / m ^{3}
 Steel: 7850 N / m ^{3}
 Aluminum: 2700 N / m ^{3}
 Bronze: 8600 N / m ^{3}
 Lead : 11400 N / m ^{3}
 Zinc: 7200 N / m ^{3}
 Iron foundry: 7250 N / m ^{3}
 Water : 1000 N / m ^{3}
 Asphalt: 1300 N / m ^{3}
 Stacked paper: 1100 N / m ^{3}
 Slate: 2800 N / m ^{3}
 Tar: 1200 N / m ^{3}
 Granite: 2800 N / m ^{3}
Specific gravity and density
The relationship between specific gravity and density is the same as that between the weight and mass of a substance. The density has to do with the level of accumulation of matter in an object or substance, ie, the amount of material that comprises; and since the specific weight is nothing more than the force with which the Earth attracts a unit of mass of said matter, it is evident that a substance whose particles are denser together, that is, more compact than others, will be attracted with more force by gravity than other more dispersed particles.