What is Density?
The density of a material, typically denoted using the Greek symbol ρ (rho), is defined as its mass per unit volume. In mathematical terms, density is the ratio of an object's mass to the space it occupies. It is an intensive property, meaning it does not depend on the quantity of the substance present.
The calculation of density is quite straightforward. However, it is important to pay special attention to the units used for density calculations. There are many different ways to express density, and not using or converting into the proper units will result in an incorrect value. It is useful to carefully write out whatever values are being worked with, including units, and perform dimensional analysis to ensure that the final result has units of mass over volume.
Note that density is also affected by pressure and temperature. In the case of solids and liquids, the change in density is typically low. However, when regarding gases, density is largely affected by temperature and pressure. An increase in pressure decreases volume, and always increases density. Increases in temperature tend to decrease density since the volume will generally increase. There are exceptions however, such as water's density increasing between 0 °C and 4 °C.
How to Use This Calculator
This flexible tool allows you to calculate any one of the three variables in the density equation as long as the other two are known.
- Find Density: Provide the mass and volume of the object.
- Find Volume: Provide the known density and the mass.
- Find Mass: Provide the density and the total volume.
ρ = m / V (to find density)
V = m / ρ (to find volume)
m = ρ × V (to find mass)
Where:
ρ is the density
m is the mass
V is the volume
Common Density Units
Below is a table of units in which density is commonly expressed. The standard SI unit is kilograms per cubic meter (kg/m³).
| Unit | Value in kg/m³ |
|---|---|
| kilogram/cubic meter | SI Unit (1) |
| kilogram/cubic centimeter | 1,000,000 |
| gram/cubic meter [g/m³] | 0.001 |
| gram/cubic centimeter [g/cm³] | 1,000 |
| kilogram/liter [kg/L] | 1,000 |
| gram/liter [g/L] | 1 |
| pound/cubic inch [lb/in³] | 27,680 |
| pound/cubic foot [lb/ft³] | 16.02 |
| pound/cubic yard [lb/yd³] | 0.5933 |
| pound/gallon (US) | 119.83 |
| pound/gallon (UK) | 99.78 |
| ounce/cubic inch [oz/in³] | 1,730 |
| ounce/cubic foot [oz/ft³] | 1.001 |
| ounce/gallon (US) | 7.489 |
| ounce/gallon (UK) | 6.236 |
Density of Common Materials
For reference, here are the approximate densities of several common materials and celestial bodies.
| Material | Density in kg/m³ |
|---|---|
| Earth's atmosphere at sea level | 1.2 |
| Water at standard temp/pressure | 1,000 |
| The Earth | 5,515.3 |
| Iron | 7,874 |
| Copper | 8,950 |
| Tungsten | 19,250 |
| Gold | 19,300 |
| Platinum | 21,450 |
| Atomic nuclei | 2.3 × 10¹⁷ |
| Black hole | above 1 × 10¹⁹ |
Frequently Asked Questions
No. Weight measures the force of gravity exerted on an object's mass, while density measures how much mass is packed into a specific volume. Two objects can have the exact same weight but entirely different densities (like a kilogram of feathers taking up much more space than a kilogram of iron).
Ice floats because it is less dense than liquid water. When water freezes, its molecules arrange themselves into a crystalline structure that actually takes up more volume than the liquid state, thereby decreasing its density.
If you compress a gas, its volume decreases while its mass remains exactly the same. Because density is mass divided by volume (m/V), a smaller volume results in a higher density.
The standard SI unit for density is kilograms per cubic meter (kg/m³). However, in many scientific disciplines, grams per cubic centimeter (g/cm³) or grams per milliliter (g/mL) are more commonly used for practical reasons.
For most substances, heating causes them to expand (volume increases). Since the mass doesn't change, the increased volume leads to a lower density. Conversely, cooling usually causes materials to contract, resulting in an increased density. Water is a notable exception between 0°C and 4°C, where it becomes denser as it warms.