How this instrument works
Density is mass divided by volume: ρ = m ⁄ V. It is an intensive property — cut a bar of aluminium in half and each piece keeps the same 2700 kg/m³, because mass and volume shrink together. That is what makes the number useful: it belongs to the material, not to the sample, so a measured value can identify an unknown solid or expose a fake.
The SI unit is the kilogram per cubic metre, and water anchors the whole scale: the gram was defined in 1795 as the mass of one cubic centimetre of water, which is why fresh water lands at a clean 1000 kg/m³ and why 1 g/cm³ and 1000 kg/m³ are the same statement. Materials lighter than that float in water; heavier ones sink. Ice, near 917 kg/m³, floats on its own liquid — a genuinely rare behaviour among substances.
Because volume grows with temperature while mass stays put, the ratio drifts as things warm: water peaks at 999.97 kg/m³ near 4 °C and thins to about 998.2 kg/m³ at room temperature. For everyday work the tabulated room-temperature value is fine; for lab work, write the temperature down next to the number.
- Enter the sample's mass in the Mass field — the unit menu takes grams, kilograms, tonnes, ounces, or pounds and converts for you.
- Enter its volume in the Volume field, in millilitres, litres, cubic metres, or gallons. For an irregular object, find this number by water displacement.
- Read the Density (kg/m³) result. Divide by 1000 if you want g/cm³, the unit most handbooks print.
- Compare against 1000 kg/m³: below it the sample floats in fresh water; above it, it sinks.
Worked example — one litre of water
Fill a measuring jug to exactly one litre and weigh it, jug subtracted: the scale reads 1 kg. One litre is 0.001 m³, so ρ = 1 ⁄ 0.001 = 1000 kg/m³ — the textbook figure for fresh water, and the very case this instrument's golden test pins down.
The round number is no accident. When France defined the gram in 1795, it chose the mass of one cubic centimetre of water, so water's density is 1 g/cm³ by construction. Weigh a litre of anything else and the comparison is immediate: 0.92 kg of cooking oil floats on water; 13.6 kg of mercury emphatically does not.
Questions
What is the formula for density?
Density equals mass divided by volume: ρ = m ⁄ V. In SI units that is kilograms over cubic metres, giving kg/m³. The same relation rearranges to m = ρ·V and V = m ⁄ ρ, which is how a tank farm estimates the mass of fuel from a fill level, and how you can weigh a liquid you can only measure by eye.
What is the density of water in kg/m³?
Very close to 1000 kg/m³. Precisely, fresh water peaks at 999.97 kg/m³ at 3.98 °C and falls to about 998.2 kg/m³ at 20 °C; seawater runs near 1025 kg/m³ because of dissolved salt. For most calculations the round 1000 is the honest working figure, and it is the value this instrument's worked example uses.
How do I convert kg/m³ to g/cm³?
Divide by 1000. A cubic metre holds a million cubic centimetres and a kilogram holds a thousand grams, so the factor between the units is exactly 1000: aluminium's 2700 kg/m³ is 2.70 g/cm³. Handbooks usually print g/cm³; engineering codes usually want kg/m³ — the same number with the decimal point moved three places.
Why does ice float on water?
Because freezing makes water expand. The ice crystal's hydrogen-bonded lattice holds molecules farther apart than they sit in the liquid, so ice comes out near 917 kg/m³ — about 8% lighter than the water it froze from. That is unusual: almost every other substance is denser as a solid, which is why lakes freeze from the top down rather than the bottom up.
How do I measure the volume of an irregular object?
Submerge it. Drop the object into a graduated container of water and read how much the level rises — that rise is the object's volume, millilitre for millilitre. This is Archimedes' displacement method, reputedly discovered while he was checking whether a royal crown was pure gold, and the reading feeds straight into the Volume field here.
Can density identify a material?
Often, within limits. Measure 19.3 g/cm³ and you are holding gold, tungsten, or very little else; 2.7 g/cm³ points strongly at aluminium. But alloying, porosity, and hollow spaces all shift the reading, so treat a matching value as strong evidence rather than proof, and confirm with a second property such as hardness or magnetism.