Specific weight

The ratio between weight and volume is called specific weight. The symbol used for specific weight is γ and the SI unit of measurement is N/m3.

\[\gamma = \frac{G}{V}=\frac{m \cdot g}{V} \tag{1}\]

where:
G [N] – weight
V [m3] – volume
m [kg] – mass
g [m/s2] – gravitational acceleration

The density ρ [kg/m3] is the ratio between mass (m) and volume (V):

\[\rho = \frac{m}{V} \tag{2}\]

Replacing the expression of the density in formula (1), we get:

\[\gamma = \rho \cdot g\]

Specific weight, unlike density, is not absolute, it depends on the value of the gravitational acceleration (g), which varies depending on altitude and latitude.

Example of specific weight (liquid): water

Temperature [°C]Specific weight [kN/m3]
09.805
59.807
109.804
159.798
209.789
259.777
309.765
409.731
509.690
609.642
709.589
809.530
909.467
1009.399
Specific weight of water

Image: Specific weight of water



Example of specific weight (gas): air

Temperature [°C]Specific weight [N/m3]
-4014.86
-2013.86
012.68
1012.24
2011.82
3011.43
4011.06
6010.4
809.81
1009.28
2007.33
Specific weight of air

Image: Specific weight of air

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