Density is mass divided by volume, and the equation rearranges to give any one of the three from the other two. This density calculator does all three directions, accepts mixed metric and imperial units on each field independently, and includes a library of common substances so you can fill in a density you do not have to hand. It also reports specific gravity and whether the material would float in water, which is usually the reason people wanted the density in the first place.
Arb Digital builds free calculators that stay in their lane, and this site has two neighbours to this page worth distinguishing. The density converter rescales a density you already have between kg/m³, g/cm³, lb/ft³ and the rest; it never touches mass or volume. The material weight calculator starts from a shape and its dimensions and returns a weight for a chosen material. This page does the thing neither of those does: it computes any one of density, mass and volume from the other two that you measured yourself, with a substance library to fall back on.
What This Density Calculator Does
Pick which quantity you want, enter the other two with the units you measured them in, and the tool converts everything to SI internally before dividing or multiplying. That internal conversion is the point of the unit selectors: weighing something in pounds and measuring it in litres is a perfectly normal situation, and it should not require you to do two conversions by hand before you can divide.
The grid gives the density in g/cm³ and lb/ft³ regardless of which quantity you solved for, plus the specific gravity — the ratio to water at 1,000 kg/m³ — and a plain float-or-sink verdict. Specific gravity is a dimensionless number, which makes it the same in every unit system, and it is the form used in most material specifications for exactly that reason.
The substance library fills the density field with a typical value when you have no measurement. Those figures are approximations: mild steel varies with alloy and heat treatment, concrete varies enormously with mix and aggregate, and timber varies with species and moisture content by more than any other common material. Treat them as a starting point, not a specification.
How to Use It
- Choose what you are solving for first. The selected field is not read, so leftover numbers in it are harmless.
- Set each unit selector independently. Mass in pounds with volume in litres is fine; the tool handles the mismatch rather than expecting you to.
- Use the true volume of the material. For a porous or loose material — sand, gravel, powder — the volume you measure includes air, and the density you get is a bulk density, not the density of the substance itself.
- Fill the density from the library only as an estimate. If the answer matters, measure a sample instead of accepting a book figure.
- Read the specific gravity for comparisons. It is unit-free, so it travels between metric and imperial documents without conversion.
The Formula: How Density Is Calculated
The definition is ρ = m/V, which rearranges to m = ρV and V = m/ρ. The SI unit is the kilogram per cubic metre, and that is the unit everything is converted into before the arithmetic happens.
Taking the defaults: 2.7 kg occupying 1 litre. A litre is 0.001 m³, so the density is 2.7 ÷ 0.001 = 2,700 kg/m³. Dividing by 1,000 gives 2.7 g/cm³, and multiplying by 0.062428 gives 168.6 lb/ft³. The specific gravity is 2,700 ÷ 1,000 = 2.7, well above 1, so the material sinks. That density is a good match for aluminium, which is why the value was chosen as the default.
The conversion factors are worth knowing because they recur. One g/cm³ is exactly 1,000 kg/m³, which means water is 1.000 g/cm³ and 1,000 kg/m³ simultaneously — an arrangement that is not a coincidence, since the kilogram was originally defined from the mass of a litre of water. One lb/ft³ is 16.0185 kg/m³. Unit definitions and correct usage are set out in NIST Special Publication 811, and the physical definitions behind them in the OpenStax section on fluids, density and pressure.
Bulk Density, True Density and Why They Differ
This is the distinction that ruins more density calculations than any other. If you fill a bucket with sand and weigh it, you have measured the bulk density of sand — the mass of grains plus the air between them, divided by the total volume. The true density of the quartz itself is around 2,650 kg/m³, but poured dry sand comes out closer to 1,600, because roughly forty percent of the bucket is air.
Neither figure is wrong; they answer different questions. Bulk density is what you want for ordering material by the tonne or working out what a truck can carry. True density is what you want for identifying a substance or predicting whether an individual grain will settle in water. Confusing the two makes a material look like something else entirely.
The same problem appears with foamed, hollow or porous materials, and with anything that traps air. It is also why a floating object's average density — the figure that matters for the buoyancy calculator — includes the sealed air inside it and is much lower than the density of the material it is made from.
Density Is Not Constant: Temperature and Pressure
Every density figure implicitly comes with a temperature. Water is at its densest at about 4 °C, close to 1,000 kg/m³, falls to roughly 997 at 25 °C, and to about 958 at boiling point. That is a four percent range across ordinary conditions, which is enough to matter in any measurement claiming better than a percent of accuracy.
Water is also famous for an anomaly: ice is less dense than the liquid it forms from, around 917 against 1,000, which is why ice floats and why lakes freeze from the top down. Almost every other substance is denser as a solid than as a liquid. The consequence for life on Earth is considerable, and the consequence for plumbing is that freezing water expands and splits pipes.
Gases are a different matter entirely. Their density depends strongly on both pressure and temperature, so quoting one without the other is meaningless. Air at sea level and 15 °C is about 1.225 kg/m³; at 10,000 metres it is roughly a third of that. Any gas density figure needs its conditions stated, which is why the library entry here names them explicitly.
Reading Specific Gravity and the Float Test
Specific gravity is density expressed as a ratio to water, so a value above 1 sinks and below 1 floats. Being dimensionless, it appears in material datasheets, mineral identification tables and fluid specifications across both unit systems without needing conversion — a genuine practical advantage over a raw density figure.
The float verdict this tool gives compares the material against fresh water at 1,000 kg/m³. Seawater at about 1,025 is slightly more forgiving, which is why a vessel floats a little higher at sea than in a river, and why the same object can float in one and sink in the other when its density sits between the two figures.
Density is also the fastest non-destructive way to distinguish materials that look alike. Gold at about 19,300 kg/m³ and brass at around 8,500 are visually similar and differ by more than a factor of two in density, which is why weighing a piece and measuring its displaced volume has been the classic authenticity test since Archimedes. For that measurement, the mass to volume converter and the cylinder volume calculator handle the geometry side.
Arb Digital builds free tools like this one because useful pages earn attention. If you want tools, calculators or content built for your own audience, we can help.
Browse All Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Confusing bulk density with true density — a bucket of gravel is mostly stone and partly air, and the two figures can differ by forty percent or more.
- Quoting a gas density without conditions — gas density depends on pressure and temperature, so a bare number describes nothing.
- Mixing mass and weight — density uses mass. A pound-force and a pound-mass are numerically equal only at standard gravity, and the distinction matters as soon as you leave it.
- Assuming a library value fits your sample — steel grades, concrete mixes and timber species vary widely, and moisture content alone can move a wood figure by a third.
- Ignoring temperature on precise work — water alone varies by about four percent between 4 °C and boiling, which swamps the resolution of any careful measurement.
Related Free Tools From Arb Digital
Density connects mass, volume and buoyancy. Convert an existing density figure with the density converter, work out the weight of a shaped piece of material with the material weight calculator, and check whether something floats with the buoyancy calculator. For the geometry, use the cylinder volume calculator or the sphere volume calculator, and for unit work the volume converter or the weight converter. Everything else is listed in the free online tools hub.
Frequently Asked Questions
The converter rescales a density you already have between units such as kg/m³, g/cm³ and lb/ft³. This page computes density, mass or volume from the other two quantities you measured, and includes a substance library for when you have no density figure at all.
The ratio of a substance's density to that of water, taken here as 1,000 kg/m³. Because it is a ratio it has no units, so it reads the same in metric and imperial documents, and any value above 1 sinks in fresh water.
Usually because the measured volume includes air. Porous, loose or hollow materials give a bulk density well below the true density of the substance. Temperature, alloy composition and moisture content account for most of the rest.
Yes. Most materials expand when heated, so density falls. Water varies by about four percent between 4 °C and boiling, and gases change far more because they respond strongly to both temperature and pressure.
Because ice is about 917 kg/m³ against roughly 1,000 for liquid water. Water is unusual in expanding as it freezes; most substances are denser as solids than as liquids and their solid form sinks.
Yes. Each field has its own unit selector, so mass in pounds with volume in litres works without any manual conversion. Everything is converted to SI internally before the calculation runs.
Mass. Density is mass per unit volume, and weight is a force that depends on local gravity. The two are numerically interchangeable only under standard gravity, which is why scientific work always specifies mass.
This tool is provided for educational and general reference use. Library densities are approximate typical values and are not material specifications for engineering, trading or assay purposes.
