Density is a physical property of matter. In a qualitative manner, density can be defined as the measure of the relative heaviness of objects with a constant volume. Density may also refer to how closely packed or crowded the material appears to be. Quantitatively, It is a ratio of mass and volume of an object.

Density and heat are inversely proportional. Adding heat energy causes molecules to move more quickly which means the material will expand and become less dense. Heat energy can change the state of a gas, liquid, or solid. Density of materials also influences the thermal resistance of materials. Less dense material are more resistive to heat flow.

## Units and Measures

The density of a material is defined as its mass per unit volume. The mass is normally measured with a scale or balance; the volume may be measured directly from the geometry of the object or by the displacement of a fluid. Hydrostatic weighing is a method that combines these two.

Following are the units of Density:

SI Units:

• kilograms per litre (kg/L)
• kilograms per cubic decimeter (kg/dm³)
• grams per millilitre (g/mL)
• grams per cubic centimeter (g/cc, gm/cc or g/cm³)

Imperial Units:

• Avoirdupois ounces per cubic inch (oz/cu in)
• Avoirdupois pounds per cubic inch (lb/cu in)
• pounds per cubic foot (lb/cu ft)
• pounds per cubic yard (lb/cu yd)
• pounds per U.S. liquid gallon or per U.S. dry gallon (lb/gal)
• pounds per U.S. bushel (lb/bu)

### Example Values

(Density per ml)

• Water - 1
• Aluminum - 2.70
• Pine wood - 0.35 - 0.50