Density is mass per unit volume: ρ = m / V, expressed in kg/m³ or g/cm³. The Toolenza calculator solves for density, mass, or volume given any two.

Reference densities worth knowing

• Water — 1,000 kg/m³ (1 g/cm³, 8.34 lb/gal). The reference point everything else compares to.
• Air at sea level — 1.225 kg/m³. About 800× less dense than water.
• Wood — 400 (balsa) to 1,200 (lignum vitae) kg/m³. Most floats; densest hardwoods sink.
• Steel — 7,850 kg/m³. Iron similar.
• Lead — 11,340 kg/m³. Why lead shielding is heavy.
• Gold — 19,300 kg/m³. The reason counterfeit detection by weight is easy.
• Osmium — 22,590 kg/m³. The densest naturally-occurring element.

Where density actually shows up

• Will it float? — anything less dense than water (1,000 kg/m³) floats in fresh water. Ice (917) floats; oak (700) floats; granite (2,700) sinks.
• Material identification — historic gold-versus-fake-gold checks: weigh in air and in water; the density math reveals adulteration.
• Concrete + structural mass — knowing density × volume gives mass for structural load calculations.
• Cooking — converting cups (volume) to grams (mass) for any ingredient. Flour density varies enough by packing (sifted vs scooped) that pro bakers always weigh.

Pitfall

Density depends on temperature and phase. Water's density peaks at 4 °C (1,000 kg/m³) and drops at higher and lower temps — which is why ice floats. For precision work, specify temperature.