What density means
Density is how much mass is packed into a given volume. A kilogram of feathers and a kilogram of lead weigh the same, but the lead takes up far less space because it's much denser. Density is a property of the material, not the object, so it's a good way to identify what something is made of.
Two units are common. Scientists and engineers use kilograms per cubic meter (kg/m³); chemistry labs often use grams per cubic centimeter (g/cm³), which is the same as grams per milliliter. In the US, pounds per cubic foot (lb/ft³) shows up in construction and shipping.
The formula
m = ρ × V
V = m ÷ ρ
1 g/cm³ = 1,000 kg/m³ = 62.43 lb/ft³
Other conversions used: 1 L = 1,000 cm³ = 0.001 m³, 1 mL = 1 cm³, 1 ft³ = 0.0283168 m³, 1 US gallon = 3.785411784 L and 1 lb = 0.45359237 kg.
Example: identifying a metal block
A block has a mass of 540 g and a volume of 200 cm³ (the default values).
| Step | Result |
|---|---|
| ρ = 540 g ÷ 200 cm³ | 2.7 g/cm³ |
| In kg/m³: 2.7 × 1,000 | 2,700 kg/m³ |
| In lb/ft³: 2,700 ÷ 16.018 | 168.6 lb/ft³ |
| Specific gravity: 2,700 ÷ 1,000 | 2.7 |
| Closest match | Aluminum |
Densities of common materials
| Material | kg/m³ | g/cm³ |
|---|---|---|
| Air (20 °C, sea level) | 1.204 | 0.001204 |
| Ethanol (20 °C) | 789 | 0.789 |
| Ice (0 °C) | 917 | 0.917 |
| Water (25 °C) | 997 | 0.997 |
| Water (4 °C, its densest) | 1,000 | 1.000 |
| Seawater (typical) | about 1,025 | about 1.025 |
| Aluminum | 2,700 | 2.70 |
| Iron | 7,874 | 7.874 |
| Copper | 8,960 | 8.96 |
| Lead | 11,340 | 11.34 |
| Gold | 19,300 | 19.3 |
Values are for pure materials near room temperature unless noted. Alloys such as steel (about 7,850 kg/m³) and brass vary with their exact mix.
Tips and common mistakes
- Mismatched units. Grams over liters gives g/L, which is the same number as kg/m³, not g/cm³.
- Hollow objects. The formula gives average density. A hollow aluminum can is far less dense overall than solid aluminum.
- Temperature matters for liquids and gases. Most substances expand when warmed, so their density drops. Air changes a lot with altitude too.
- Trapped air bubbles during water displacement make the volume look bigger and the density smaller. Tap the object to release them.
Frequently asked questions
What is the formula for density?
Density = mass ÷ volume, written ρ = m ÷ V. Rearranged, mass = density × volume and volume = mass ÷ density. In SI units density is in kilograms per cubic meter (kg/m³); in the lab, grams per cubic centimeter (g/cm³) is more common.
How do I convert g/cm³ to kg/m³?
Multiply by 1,000. Water is about 1 g/cm³, which is 1,000 kg/m³. A cubic meter holds a million cubic centimeters, and a kilogram is 1,000 grams, so the factor works out to 1,000.
What is the density of water?
Pure water is densest at about 4 °C, where it's very close to 1,000 kg/m³ (1 g/cm³). At room temperature, 25 °C, it's about 997 kg/m³. Seawater is denser, around 1,025 kg/m³, because of the dissolved salt.
How do I find the volume of an irregular object?
Use water displacement. Fill a measuring container, note the level, submerge the object fully and read the new level. The rise is the object's volume; 1 mL equals 1 cm³. Then weigh the object and divide.
Will it float?
An object floats in water if its average density is less than the water's, about 1,000 kg/m³ (1 g/cm³). Ice at about 917 kg/m³ floats with roughly 90% of it under the surface. Steel ships float because their hollow shape makes their average density lower than water.
What is specific gravity?
Specific gravity is density compared with water, so it has no units. This calculator divides by 1,000 kg/m³. Aluminum, at 2,700 kg/m³, has a specific gravity of 2.7.
Rates and figures last checked October 2026.
This calculator gives estimates for planning. Check current rates and product labels before you buy, list or file.