Calculate density, mass or volume — solve for any one of the three variables using ρ = m/V. Supports multiple unit conversions.
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Density is the mass of a substance per unit volume, expressed as ρ = m/V. It measures how tightly packed matter is. Water has a density of 1 g/cm³ (1,000 kg/m³). Steel is about 7.85 g/cm³. Air at sea level is about 1.225 kg/m³. Objects denser than the surrounding fluid sink; less dense objects float.
Water: 1.00 g/cm³. Ice: 0.92 g/cm³ (floats on water). Aluminium: 2.70 g/cm³. Iron: 7.87 g/cm³. Lead: 11.34 g/cm³. Gold: 19.32 g/cm³. Wood (oak): 0.75 g/cm³. Concrete: 2.3 g/cm³. Air: 0.001225 g/cm³. Diamond: 3.51 g/cm³.
For most materials, density decreases as temperature increases because thermal expansion increases volume while mass stays constant. Water is a notable exception — it is densest at 4°C and less dense both above and below this temperature. This is why ice floats and lakes freeze from the top down, allowing aquatic life to survive winter.
Relative density (specific gravity) is the ratio of a substance's density to a reference density — usually water at 4°C (1.000 g/cm³) for liquids/solids, or air at STP for gases. It is dimensionless. If SG > 1, the material is denser than water and sinks; if SG < 1, it floats.
Density is fundamental to buoyancy calculations (ship design, submarines), aerospace (weight vs strength trade-offs), fluid dynamics, material selection, food science (measuring sugar content in beverages with hydrometers) and geology (identifying minerals). It is one of the most widely used physical properties in engineering.
Osmium (Os) is the densest naturally occurring element at 22.59 g/cm³, followed closely by iridium at 22.56 g/cm³. By comparison, gold is 19.32 g/cm³ and lead is 11.34 g/cm³. Osmium is about twice as dense as lead and 22 times denser than water.
Use the water displacement method: measure the volume of water displaced when the object is fully submerged. Volume displaced = volume of object. Then divide the object's mass by this volume. Archimedes famously used this principle to verify the purity of a gold crown without melting it.
Population density is the number of people per unit area — people per km² or per mile². It is calculated as: population ÷ area. Bangladesh is one of the world's most densely populated countries at ~1,100 people/km²; Mongolia is among the least dense at ~2 people/km². While different from physical density, the same ρ = n/V formula applies.
