Specific Weight

γ = ρ g

Weight per unit volume. In SI, freshwater γ ≈ 9.81 kN/m³; in US customary ≈ 62.4 lb/ft³. Specific gravity is γ/γ_water = ρ/ρ_water. Hydrostatic pressure uses p = γh. On a smaller g (the Moon), γ shrinks even if ρ is unchanged.

$γ$ (N/m³): Specific weight
$ρ$ (kg/m³): Density
$g$ (m/s²): Gravitational acceleration

Step-by-step solved example

ρ = 1000 kg/m³, g = 9.81 m/s². Find γ.

γ = ρg. Hydrostatic p = γh uses specific weight directly.

1. Definition
γ = ρg = 1000 × 9.81 = 9810 N/m³.
$γ = 9810 N/m^{3}$
2. kN
γ = 9.81 kN/m³, the standard FE water value.

Answer: 9.81 kN/m³

10 practice questions

0/10 correct

1.γ of water in SI is about

2.ρ = 800 kg/m³. γ ≈

3.Specific gravity of a fluid is

4.US customary γ_water is about

5.ρ_Hg = 13600 kg/m³. γ ≈

6.Units of γ are

7.On the Moon (smaller g), γ_water would be

8.Hydrostatic p = γh uses

9.SG = 1.26. γ ≈

10.Density ρ equals