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Unit Weight / Density Calculator

Calculate the weight of materials from volume and density. Includes built-in density reference for steel, concrete, timber, soil, water, and more.

Concrete Engineering Engineers, contractors, QS professionals Commercial Intent: HIGH

Material

Volume

Volume Unit

Custom Density (optional) — kg/m³

Engineering Formulas

Weight from Density & Volume

W = ρ × V

W: Weight (kg)

ρ: Density (kg/m³)

V: Volume (m³)

Specific Weight

γ = ρ × g

γ: Specific weight (kN/m³)

ρ: Density (kg/m³)

g: Gravity (9.81 m/s²)

Worked Example

Steel Beam Weight Calculation

material: steelvolume: 0.05volumeUnit: m³

Given

Material: Structural Steel (ρ = 7,850 kg/m³), Volume: 0.05 m³

Formula

W = ρ × V = 7,850 × 0.05

Weight

W = 392.50 kg

Tonnes

392.50 / 1000 = 0.393 tonnes

Result: A steel member with 0.05 m³ volume weighs approximately 393 kg or 0.393 tonnes.

Engineering Notes

Always verify material densities against project specifications and test reports.

For structural calculations, use characteristic values with appropriate partial safety factors.

Timber densities vary significantly with moisture content — use values at 12% moisture content for design.

The density of concrete varies with aggregate type, w/c ratio, and admixtures.

For reinforced concrete, add 1-2% to account for steel reinforcement weight.

Assumptions

• Densities are nominal values at standard temperature and pressure

• Material is assumed homogeneous and void-free

• Moisture content affects actual density (especially for timber and soil)

• Steel density assumes solid section (not hollow)

Common Mistakes

✕ Confusing density (kg/m³) with specific weight (kN/m³) — divide by 101.97 to convert

✕ Using wet density when dry density is required (especially for soil)

✕ Forgetting to convert volume units (e.g., using litres as m³)

✕ Not accounting for reinforcement in reinforced concrete weight

✕ Using incorrect density for alloyed vs pure metals

Frequently Asked Questions

What is the difference between density and unit weight?

Density (ρ) is mass per unit volume (kg/m³). Unit weight (γ) is weight per unit volume (kN/m³). They are related by γ = ρ × g where g = 9.81 m/s².

What is the density of structural steel?

Structural steel has a density of approximately 7,850 kg/m³. This is equivalent to 78.5 kN/m³ in unit weight terms, or 490 lb/ft³ in imperial units.

How much does 1 m³ of concrete weigh?

Normal weight concrete weighs approximately 2,400 kg/m³ (23.5 kN/m³). Lightweight concrete is about 1,800 kg/m³, and heavyweight concrete can reach 2,600 kg/m³.

What is the density of water in kg/m³?

Fresh water has a density of 1,000 kg/m³ at 4°C. Sea water is slightly denser at approximately 1,025 kg/m³. This is why ships float higher in sea water.

How do I calculate the weight of a steel beam?

Multiply the beam's volume (cross-sectional area × length) by the density of steel (7,850 kg/m³). Our calculator can do this for you — just select steel and enter the volume.

What is the unit weight of soil?

Dry sand is about 16 kN/m³, clay is 18–20 kN/m³, and gravel is 18–22 kN/m³. The unit weight varies significantly with moisture content and compaction.

Can I use custom densities?

Yes — enter a custom density value in the optional field. This overrides the selected material's default density for non-standard materials.

What volume units are supported?

We support cubic meters (m³), litres (L), cubic feet (ft³), cubic yards (yd³), and US gallons. Results are always shown in kg and tonnes.