Peso Específico
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
γ = ρg
About this calculator
The specific weight calculator (γ) determines the weight per unit volume of a material using the formula γ = ρ · g, where ρ is the density and g is the acceleration due to gravity (standard 9.81 m/s²). The result is expressed in N/m³ (SI) or other compatible units. This tool is useful for engineers, technicians, and students who need to calculate structural loads, fluid buoyancy, or tank sizing.
How it works: enter the material density (kg/m³) and local gravity (m/s², optional). The calculation multiplies these values to obtain the specific weight. For example, water has a density of 1000 kg/m³ and a specific weight of approximately 9810 N/m³ (assuming g = 9.81 m/s²). The calculator also allows unit conversion to kN/m³, kgf/m³, or lb/ft³.
When to use: in dam design, hydrostatic pressure calculation, slope stability analysis, pipeline projects, and any situation where the weight force per volume of material is relevant. It is essential for determining the load exerted by a fluid on submerged surfaces or the buoyancy of objects.
Cautions: density must be measured or obtained from reliable sources, as it varies with temperature and pressure. Local gravity may differ from 9.81 m/s² at high altitudes or on other planets. Check units: use kg/m³ for density and m/s² for gravity; the result will be in N/m³. For conversions, remember that 1 N/m³ = 0.10197 kgf/m³.
Frequently asked questions
What is the difference between specific weight and density?
Density is mass per unit volume (kg/m³). Specific weight is weight per unit volume (N/m³), which depends on gravity. The relationship is γ = ρ · g.
Can I use the calculator for gases?
Yes, but gas density varies greatly with temperature and pressure. Use the density under specific conditions (e.g., air at 20°C and 1 atm has ρ ≈ 1.2 kg/m³).
How do I convert the result to kgf/m³?
Divide the value in N/m³ by 9.80665 (1 kgf = 9.80665 N). Example: 9810 N/m³ ÷ 9.80665 ≈ 1000 kgf/m³.
What happens if I change the gravity value?
The specific weight changes proportionally. In locations with lower gravity (e.g., Moon, 1.62 m/s²), the specific weight will be about 1/6 of the Earth value.
What is the standard SI unit?
Newton per cubic meter (N/m³). kN/m³ is also common (1 kN/m³ = 1000 N/m³).