Foam density follows the basic relationship:

For a rectangular specimen, V=L×W×T. The calculator supports direct volume or measured dimensions.

Choose the sample method, enter cured sample mass and volume or dimensions, then calculate kg/m³, g/cm³ and lb/ft³. Use reverse mass/volume calculations only as planning estimates unless the product specification defines nominal density clearly.

Use a representative fully cured sample and a test method appropriate to the product. Irregular edges, surface skins, open cells, trapped voids and moisture can influence apparent density. ASTM D1622/D1622M is a widely used reference for apparent density of rigid cellular plastics.

Furniture foam is often marketed by density because density can correlate with material amount and, within a product family, durability. Density is not the same as firmness. Indentation force/deflection and foam formulation affect how soft or firm the foam feels.

In North American upholstery and spray-foam contexts, values such as 1.8 or 2 lb often refer to pounds per cubic foot. In other markets, numbers such as 32 or 40 may refer to kg/m³. Always confirm the unit before comparing grades.

A nominal 6 lb/ft³ foam contains much more mass per unit volume than 2 lb/ft³ foam, but the products may also serve completely different functions. Higher density does not automatically mean “better” for every insulation, cushioning or structural application.

1 lb/ft³ is approximately 16.0185 kg/m³. The calculator reports both so product data from different regions can be compared on the same basis.

Density alone cannot reliably predict service life, firmness or expansion yield. Cell structure, chemistry, load history, UV exposure, temperature and manufacturing quality all matter. Product-specific manufacturer data is more useful than a generic internet promise that “X density lasts Y years.”

Because foam is compressible, do not crush the specimen while measuring dimensions. Small samples with irregular edges can create large relative volume error. Use the test method and specimen conditioning required by the relevant standard.

A cured foam sample measures 20 cm × 10 cm × 5 cm, giving 1000 cm³ volume. If it weighs 32 g, density is 0.032 g/cm³ = 32 kg/m³ ≈ 2.0 lb/ft³. This is why the same sample can be described as “32 density” or “2 lb foam” in different unit systems.

Upholstery foams may be marketed around roughly 20–60+ kg/m³, while rigid or specialty structural foams can occupy very different ranges. Open-cell and closed-cell spray foams are also commonly specified in lb/ft³. Product categories overlap, so use manufacturer data rather than assuming one universal band.

Do not compress the sample while measuring, do not mix kg/m³ with lb/ft³ labels, and do not treat foam density as firmness. A dense soft foam and a less-dense firm foam are both possible because formulation and cell structure matter.