Specific weight is obtained by multiplying density by the acceleration of gravity
9,80665 m/s² (Earth's g)
Density (symbol ρ, rho) is the ratio between a body's mass and its volume, expressed in kg/m³: it is an intrinsic property of the material, which does not change depending on location. Specific weight (symbol γ, gamma) is instead the ratio between a body's weight (a force, due to gravity) and its volume, expressed in N/m³: it therefore depends on local gravitational acceleration, and would technically be different on the Moon or Mars, even though the material's density remains identical.
The relationship between the two quantities comes from Newton's second law (weight = mass × gravity), applied per unit of volume:
To go back from specific weight to density, perform the inverse operation, dividing by 9.80665:
Specific weight is widely used in civil and geotechnical engineering, for example to calculate the thrust exerted by soil or a liquid on a structure (retaining walls, dams), where what matters is the actual force exerted by the material's weight, not just its mass. Density, on the other hand, remains the reference quantity in physics, chemistry, and most general scientific contexts.