Density

Density is mass per unit volume, one of the most used properties in materials science and fluid mechanics. The SI unit is kilograms per cubic metre (kg/m³), and fresh water near 4 °C lands almost exactly at 1000 kg/m³, which equals 1 g/cm³, 1 g/mL, and about 62.428 lb/ft³. That coincidence is deliberate: the original gram was defined as the mass of one cubic centimetre of water, so the numerical match became a design choice rather than an accident.

Engineers pick units by context. Chemistry and laboratory work use g/cm³ or g/mL because sample masses are small and volumes are measured in cc. Process plants and petroleum engineering work in kg/m³ or API gravity — an offset and inverted scale where lighter hydrocarbons get higher API numbers. US construction uses pounds per cubic foot for aggregate, concrete, and structural fill. Fuel and paint spec sheets often list pounds per US gallon because that matches how the material is purchased and billed.

Quick reference points help calibrate intuition. Lead sits at roughly 11.34 g/cm³ (708 lb/ft³); uranium at 19.1 g/cm³; gold at 19.3 g/cm³. Structural steel comes in at 7.85 g/cm³ (490 lb/ft³), aluminium at 2.70 g/cm³ (168 lb/ft³), normal-weight concrete at 2.4 g/cm³ (150 lb/ft³), and lightweight concrete at 1.7 to 1.9 g/cm³. Most finished woods range 0.4 to 0.9 g/cm³, which is why they float.

Density-based conversions underpin buoyancy, sinking, and flotation calculations via Archimedes' principle: an object submerged in a fluid experiences an upward force equal to the weight of displaced fluid. That single relationship drives ship design, hydrometers, and why ice (about 0.92 g/cm³) floats on liquid water.

Our converter supports eight density units. It uses exact-factor arithmetic (1 lb = 0.45359237 kg, 1 ft = 0.3048 m exactly), so computed conversions match reference tables published by NIST, ASTM, and petroleum-industry sources without compounding rounding error. The numbers you get here line up with what a certified lab report will say.