Density is the ratio of a material’s mass to the volume it occupies, expressed in kilograms per cubic metre (kg/m³). In construction, density largely determines the weight of a structure and plays a key role in thermal insulation, sound insulation and load-bearing capacity.
Formula and units
The formula is straightforward:
ρ = m / V
where ρ (rho) is the density in kg/m³, m is the mass in kg and V the volume in m³. Sometimes g/cm³ is used instead — water has a density of 1,000 kg/m³ or 1 g/cm³.
Application
Density matters for several building tasks:
- Structural calculations — the self-weight of floors, walls and roofs equals density × volume
- Thermal insulation — low-density materials (mineral wool, EPS, glass wool) insulate well because they contain a lot of air
- Sound insulation — dense, heavy materials (concrete, brick) block both impact and airborne sound (mass law)
- Foundation design — determines the weight of the superstructure and the soil bearing capacity required
- Logistics and lifting — cranes and trucks are selected by weight per piece
Density at a glance
| Material | Density (kg/m³) |
|---|---|
| Reinforced concrete | 2,400 – 2,500 |
| Brick | 1,600 – 2,000 |
| Wood (spruce) | 450 – 550 |
| Steel | 7,850 |
| Aluminium | 2,700 |
| Glass | 2,500 |
| Mineral wool | 30 – 200 |
| EPS insulation | 15 – 40 |
| Water | 1,000 |
| Air | 1.2 |
Bulk density and absolute density
For porous materials (brick, concrete, insulation), one distinguishes between:
- Bulk density — including pores, i.e. how the material actually weighs
- Absolute density — only the mass of the solid material itself, without air
For insulation materials, bulk density is what determines performance.
Related terms
- Mass
- Volume
- Insulation
- Load
- Building physics
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