Density Calculator
Density is mass per unit volume. Enter any two of the three values — mass, volume, or density — and this calculator solves the third, converting between kg/m³, g/cm³, and lb/ft³ automatically. A table of common material densities is below for quick reference.
How density works
Density tells you how much matter is packed into a given space. A block of lead and a block of foam can be the same size, yet the lead is far heavier because its atoms are heavier and more tightly packed — it has a higher density. The relationship is a simple ratio: divide the mass by the volume and you get density. Because it is a ratio, the answer depends entirely on the units, so keeping mass, volume, and density in matching systems (or letting the selects convert for you) is the single most important step.
How it’s calculated
The calculator works in base SI units internally: grams for mass and cubic centimeters for volume, giving density in g/cm³, then converts to the display units. The core relationship is ρ = m ÷ V. To solve for mass it uses m = ρ × V; to solve for volume it uses V = m ÷ ρ. The "compared to water" line divides your density by 1000 kg/m³, the reference density of water, which also equals specific gravity.
Results update as you type and assume a uniform, solid sample at everyday temperatures. Gas density varies strongly with temperature and pressure — use with care.
Worked example
A sample has a mass of 200 g and a volume of 250 cm³. Its density is 200 ÷ 250 = 0.8 g/cm³, which is 800 kg/m³ or about 49.9 lb/ft³. Because that is below water’s 1000 kg/m³, the sample would float — consistent with a light hardwood or a dense plastic.
Common material densities
| Material | kg/m³ | g/cm³ |
|---|---|---|
| Air (sea level) | 1.2 | 0.0012 |
| Cork | 240 | 0.24 |
| Pine (softwood) | 500 | 0.50 |
| Water (4°C) | 1,000 | 1.00 |
| Concrete | 2,400 | 2.40 |
| Aluminum | 2,700 | 2.70 |
| Iron | 7,874 | 7.87 |
| Copper | 8,960 | 8.96 |
| Lead | 11,340 | 11.34 |
| Gold | 19,300 | 19.30 |
Approximate values at room temperature; alloys and moisture content shift these figures.
Common mistakes
- Mixing unit systems — putting mass in grams and volume in cubic feet without converting gives a meaningless number.
- Confusing density with weight; a heavy object can be low-density if it is simply large.
- Using gas densities from a table without checking the stated temperature and pressure.
- Forgetting that hollow or porous objects have a lower effective (bulk) density than the solid material.
Where it is used
- Identifying materials and checking purity (gold vs. gold-plated, for example).
- Buoyancy questions — will it float or sink relative to water at 1000 kg/m³?
- Engineering and shipping, where mass and volume both drive cost.
- Chemistry lab work converting between mass and volume of solutions.
Frequently asked questions
What is the formula for density?
Density (ρ) equals mass (m) divided by volume (V): ρ = m ÷ V. Rearranged, mass = ρ × V and volume = m ÷ ρ. This calculator solves whichever value you leave blank once you provide the other two.
What units should I use for density?
The SI unit is kilograms per cubic meter (kg/m³). Chemistry and everyday work often use grams per cubic centimeter (g/cm³), where 1 g/cm³ = 1000 kg/m³. US trades use pounds per cubic foot (lb/ft³), where 1 lb/ft³ ≈ 16.02 kg/m³. The unit selects handle the conversion for you.
Why does 1 g/cm³ equal 1000 kg/m³?
A cubic meter holds 1,000,000 cubic centimeters, and a kilogram is 1000 grams. So 1 g/cm³ = 1 g ÷ 1 cm³ = (0.001 kg) ÷ (0.000001 m³) = 1000 kg/m³. Water is the classic example: about 1 g/cm³, or 1000 kg/m³.
Does temperature change density?
Yes. Heating most materials expands their volume, which lowers density; cooling raises it. The effect is small for solids and liquids but large for gases, whose density depends strongly on both temperature and pressure. Water is a famous exception, reaching maximum density near 4°C.
How do I find density if I only know weight?
On Earth, weight in pounds-force or newtons is proportional to mass, so you can treat a scale reading in grams or kilograms as mass for density purposes. If your scale reads in pounds, that is technically pounds-mass and works directly in lb/ft³ once you also measure volume in cubic feet.