Density Calculator
Calculate density, mass, or volume from the other two, and compare the result against water and common materials to see what would float.
Como usar esta calculadora
- 1Choose whether to solve for density, mass, or volume.
- 2Enter the two values you know — mass in kilograms, volume in litres.
- 3Read the density in kg/m³ and g/cm³, and check the table to see what it floats on and what it sinks in.
Como funciona
Density
density = mass ÷ volume mass = density × volume volume = mass ÷ density SI unit: kg/m³ (water ≈ 1000 kg/m³ = 1 g/cm³) specific gravity = density ÷ density of water
Density is how much mass is packed into a given volume, and it is an intrinsic property of a material — a gram of gold and a tonne of gold have exactly the same density. It decides whether an object floats: anything less dense than the fluid around it rises, anything denser sinks. Because it is intrinsic, density is also one of the quickest ways to identify a material or test its purity.
Exemplo resolvido
A 1-litre (0.001 m³) block with a mass of 2.7 kg has a density of 2.7 ÷ 0.001 = 2,700 kg/m³, or 2.7 g/cm³ — the density of aluminium. Being 2.7 times denser than water, it sinks.
Density Calculator: o guia completo
Why some things float
An object floats when it is less dense than the fluid it sits in, and sinks when it is denser. This is Archimedes' principle in its simplest form: the fluid pushes up with a force equal to the weight of the fluid the object displaces, and if the object weighs less than that displaced fluid, the upward push wins. Density is just the bookkeeping that decides the outcome.
It is why a steel ship floats even though steel is eight times denser than water. The ship is not solid steel — it is mostly air-filled space, so its average density, hull plus enclosed air, is well below water's. Change that average by letting water in, and the same ship sinks. Floating is always about average density, not the material alone.
Specific gravity, the dimensionless shortcut
Specific gravity is density measured against water: a material's density divided by 1,000 kg/m³. Because it is a ratio, it has no units and is the same number in any measurement system, which makes it convenient for quick comparisons. A specific gravity above 1 sinks in water; below 1 floats.
It is widely used precisely because it is so practical. Winemakers and brewers use a hydrometer reading of specific gravity to track fermentation; gemmologists use it to distinguish a diamond from a fake; geologists use it to identify minerals. In each case a single density measurement, expressed against water, is a fast and reliable fingerprint.
Density as a purity test
Because density is intrinsic and precisely known for pure substances, measuring it is one of the oldest ways to check what something is made of. Archimedes' famous problem — was the king's crown pure gold or adulterated with silver? — is a density problem: gold is far denser than silver, so measuring the crown's mass and its volume (by the water it displaces) reveals any cheating.
The same logic is everywhere today. A density measurement flags counterfeit coins and bullion, confirms the concentration of a battery's acid, checks whether a plastic is the grade specified, and reveals the alcohol content of a spirit. Two easy measurements, mass and volume, yield a number that pure materials cannot fake.
Perguntas frequentes
How do I calculate density?
Divide mass by volume: density = mass ÷ volume. In SI units, a mass in kilograms divided by a volume in cubic metres gives density in kg/m³. Water is about 1,000 kg/m³, which is the same as 1 g/cm³.
Will my object float or sink in water?
Compare its density to water's 1,000 kg/m³. Less dense floats, denser sinks. For a hollow object like a boat, use its average density — total mass divided by total volume including any enclosed air — which is why steel ships float.
What is specific gravity?
The ratio of a material's density to that of water, so it has no units. A specific gravity of 2.7 means the material is 2.7 times denser than water. Above 1 sinks, below 1 floats. It is widely used in brewing, gemmology, and geology as a quick material test.
Does the amount of a substance change its density?
No. Density is intrinsic — a small sample and a large block of the same pure material have identical density. That is what makes it useful for identifying materials: the number depends on what something is, not how much of it you have.