What is specific weight?

Specific weight (γ) is the weight per unit volume of a material: γ = ρ × g, where ρ is density (kg/m³) and g is gravitational acceleration (m/s²). The SI unit is N/m³. It differs from density, which is mass per volume, not weight per volume.

What is the specific weight of water?

Fresh water at 4 °C has a density of 1000 kg/m³. At standard gravity (9.81 m/s²), its specific weight is 9810 N/m³ (≈ 9.81 kN/m³), or about 62.4 lbf/ft³. This value is widely used as a reference in fluid mechanics.

How is specific weight different from specific gravity?

Specific gravity (SG) is a dimensionless ratio of a material's density to that of water (ρ_water ≈ 1000 kg/m³). Specific weight is an actual force-per-volume measurement with units (N/m³ or lbf/ft³). You can convert: γ = SG × γ_water.

What units does this calculator use?

Input density is in kg/m³. Gravity is in m/s². The primary output is N/m³ (Newtons per cubic meter, SI standard). The secondary output is lbf/ft³ (pounds-force per cubic foot, US customary). Conversion: 1 lbf/ft³ ≈ 157.09 N/m³.

Can I use this for soil and geotechnical work?

Yes. Dry soil typically has a unit weight of 14–18 kN/m³; saturated soil 18–22 kN/m³. Enter the bulk density of your soil sample and this calculator gives γ directly for use in lateral pressure or settlement formulas.

Why does specific weight change on other planets?

Specific weight γ = ρ × g, so it scales linearly with gravitational acceleration. A material's density (ρ) stays the same regardless of planet, but g changes. On the Moon (g ≈ 1.62 m/s²) water's specific weight drops from 9810 N/m³ to about 1620 N/m³.

Specific Weight Calculator

Name: Specific Weight Calculator
Availability: InStock
Author: Nham Vu

Enter material density and gravitational acceleration to compute specific weight (γ = ρ × g) in N/m³ and lbf/ft³. Includes a reference table for water, steel, concrete, and more.

Input Parameters

Material / Fluid

Gravitational Acceleration

Result

Select a material and click Calculate.

Specific Weight Reference (g = 9.81 m/s²)

Material	ρ (kg/m³)	γ (kN/m³)	γ (lbf/ft³)
Fresh water (4 °C)	1 000	9.81	62.4
Seawater	1 025	10.06	64.0
Mercury	13 600	133.4	848.7
Crude oil	870	8.53	54.3
Structural steel	7 850	77.0	490.0
Normal concrete	2 400	23.5	149.8
Dry soil (typical)	1 800	17.7	112.4
Limestone	2 700	26.5	168.5
Aluminum	2 700	26.5	168.5
Softwood (pine)	600	5.89	37.5
Air (sea level)	1.225	0.012	0.077

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Summary

Enter material density and gravitational acceleration to compute specific weight (γ = ρ × g) in N/m³ and lbf/ft³. Includes a reference table for water, steel, concrete, and more.

How it works

Select a material preset or choose "Custom" and enter density in kg/m³.
Adjust gravitational acceleration if needed (default 9.81 m/s² for Earth).
Click Calculate to compute specific weight γ = ρ × g.
Result is shown in N/m³ (SI) and lbf/ft³ (imperial).
Use the reference table below to compare with common materials.

Use cases

Determine the hydrostatic pressure exerted by a column of fluid (p = γ × h).
Compute lateral earth pressure in geotechnical and retaining-wall design.
Convert material density to unit weight for structural load calculations.
Verify specific weight of concrete or soil in civil engineering problems.
Compare the weight density of fluids when designing tanks and pipelines.
Support buoyancy and stability calculations for ships and submerged structures.
Check unit weight values for academic physics or engineering homework.
Explore how gravity on other planets changes specific weight for the same material.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu