Specific Weight Calculator

Specific weight relates density to gravitational force per unit volume:

$$\gamma = \rho g$$

This quantity appears directly in the hydrostatic pressure equation:

$$P = \gamma h$$

where h is the depth below the free surface. This makes specific weight the natural quantity for calculating pressures in fluids at rest — each meter of depth adds a pressure equal to the specific weight.

Key relationships and properties:

• Hydrostatic pressure: $$P = \gamma h = \rho g h$$. Water with γ ≈ 9810 N/m³ produces approximately 9.81 kPa per meter of depth, or about 1 atm (101.3 kPa) at 10.33 m depth.
• Buoyant force: The buoyant force on a submerged object equals $$F_b = \gamma V_{\text{displaced}}$$, which is Archimedes' principle expressed using specific weight.
• Location dependence: Since g varies with altitude and latitude (from about 9.78 m/s² at the equator at sea level to 9.83 m/s² at the poles), specific weight varies accordingly. On the Moon (g ≈ 1.62 m/s²), the same fluid would have about 1/6 its terrestrial specific weight.
• Common values: Freshwater at 20°C has γ ≈ 9790 N/m³ (9.79 kN/m³), seawater ≈ 10,060 N/m³ (10.06 kN/m³), mercury ≈ 132,900 N/m³ (132.9 kN/m³), air ≈ 11.8 N/m³.

In engineering practice, specific weight is often tabulated in kN/m³ or lb/ft³. The standard value for water is commonly taken as 9.81 kN/m³ (62.4 lb/ft³) for design calculations.

The calculator also computes the hydrostatic pressure at 1 meter depth, which numerically equals the specific weight in Pa. This provides a quick reference for pressure-depth calculations in hydraulic engineering.

The calculated specific weight tells you the weight force per unit volume of the fluid. For water at standard conditions, γ ≈ 9810 N/m³ (9.81 kN/m³). The hydrostatic pressure at 1 m depth numerically equals γ in pascals. For engineering calculations, multiply γ by any depth h to find the gauge pressure at that depth: $$P = \gamma h$$. This is the foundation of all hydrostatic analysis in civil and hydraulic engineering.