Density
Mass per volume.
What does Density mean?
Density is a fundamental physical property that describes how much mass is contained in a given volume of a substance. It is commonly expressed in kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³). Density determines whether an object sinks or floats in a fluid and is widely used in material science, engineering, chemistry, and physics to identify substances and predict their behavior.
How to calculate Density
Density is calculated with the formula: ρ = m / V, where ρ (rho) is density, m is mass, and V is volume. For example, if an object has a mass of 1,000 kg and occupies a volume of 1 m³, its density is 1,000 / 1 = 1,000 kg/m³. To convert to g/cm³, divide by 1,000 — so 1,000 kg/m³ equals 1.0000 g/cm³, which is the density of water.
FAQ
Pure water at 4°C has a density of approximately 1,000 kg/m³ (or 1.0000 g/cm³). This value is often used as a reference point — substances with a density greater than water sink, while those with lower density float.
For irregular objects, use the water displacement method: submerge the object in a graduated container of water and measure the rise in water level. The volume of water displaced equals the volume of the object.
Density is an absolute measure (mass per unit volume), while specific gravity is a dimensionless ratio comparing a substance's density to the density of a reference substance (usually water at 4°C). A specific gravity of 2.0 means the substance is twice as dense as water.
Yes. Most substances expand when heated, increasing their volume while mass stays the same, which decreases density. Water is a notable exception — it reaches maximum density at 4°C and becomes less dense as it cools toward 0°C, which is why ice floats.
Engineers use density to select materials (e.g., lightweight aluminum for aircraft), design buoyant structures (ships, submarines), calculate loads and stresses, and determine fluid flow characteristics in piping and HVAC systems.
Related calculators
- Force— Mass times acceleration.
- Pressure— Force per area.
- Kinetic Energy— Energy of motion.
- Ohm's Law— Voltage-current-resistance relation.