Free · No sign-up · Runs entirely in your browser
Calculate density, mass or volume from the other two — with specific gravity and a straight answer on whether the material floats.
Choose what to solve for, then fill in the other two. The calculated field is greyed out.
| Material | Density |
|---|---|
| Water (4°C) | 1,000 kg/m³ |
| Concrete | 2,300–2,400 kg/m³ |
| Steel | 7,850 kg/m³ |
| Aluminium | 2,710 kg/m³ |
| Timber (hardwood) | 600–900 kg/m³ |
| Air (sea level) | 1.225 kg/m³ |
| Gold | 19,300 kg/m³ |
| Petrol | ~740 kg/m³ |
| Property | Value |
|---|
One formula, rearranged. The calculator asks which value you want so there is no ambiguity about what it is solving.
| Quantity | SI unit | Also written as |
|---|---|---|
| Density | kg/m³ | g/cm³, g/mL, kg/L |
| Mass | kg | g, mg, tonnes |
| Volume | m³ | L, mL, cm³ |
Specific gravity is density expressed relative to fresh water. It has no units, which is what makes it convenient — and it answers one question immediately.
Typical material densities (approximate)
| Material | Density (kg/m³) | Specific gravity | Floats in fresh water? |
|---|---|---|---|
| Balsa wood | 160 | 0.16 | Yes |
| Pine (softwood) | 510 | 0.51 | Yes |
| Petrol | 740 | 0.74 | Yes |
| Hardwood | 900 | 0.90 | Yes |
| Ice | 917 | 0.92 | Yes |
| Olive oil | 920 | 0.92 | Yes |
| Fresh water | 1,000 | 1.00 | Neutral |
| Sea water | 1,025 | 1.02 | No |
| Brick | 1,900 | 1.90 | No |
| Concrete | 2,400 | 2.40 | No |
| Glass | 2,500 | 2.50 | No |
| Aluminium | 2,700 | 2.70 | No |
| Steel | 7,850 | 7.85 | No |
| Copper | 8,960 | 8.96 | No |
| Lead | 11,340 | 11.34 | No |
| Gold | 19,320 | 19.32 | No |
Indicative values at about 20 °C. Timber, concrete, brick and soil vary substantially with species, grade, mix and moisture — use supplier or engineering data where accuracy matters.
Steel has a specific gravity of 7.85, so a solid block of it sinks immediately. Yet ships made of it float, and the reason is worth understanding because it shows what density actually measures.
Archimedes' principle says the same thing from the other direction: an object floats when it displaces a weight of water equal to its own weight. A hull shaped to displace a lot of water for its mass will float; the same steel rolled flat will not.
This is also why the density figures in the table above are for solid material. A brick has a density of about 1,900 kg/m³, but a pallet of bricks with air gaps between them has a much lower bulk density — which is the number that matters when you are working out what a truck can carry.
Almost every substance gets denser as it cools, right up to the point it solidifies. Water does not, and life on Earth depends on the exception.
| Temperature | Density |
|---|---|
| 0 °C | 999.84 kg/m³ |
| 4 °C | 999.97 kg/m³ |
| 10 °C | 999.7 kg/m³ |
| 20 °C | 998.21 kg/m³ |
| 25 °C | 997.05 kg/m³ |
| 40 °C | 992.22 kg/m³ |
| 80 °C | 971.79 kg/m³ |
| 100 °C | 958.35 kg/m³ |
Water reaches maximum density at about 4 °C and then becomes less dense as it cools further. Ice at 0 °C is around 917 kg/m³ — roughly 8% lighter than the liquid it froze from.
It also explains why "1 litre = 1 kg" is an approximation rather than a rule. At 20 °C a litre of water is about 998 g. Close enough for most work, and worth knowing when it is not.
Mass is easy — put it on scales. Volume is the hard part for anything that is not a neat shape.
| Object | How to find the volume |
|---|---|
| Regular shape | Measure and calculate — the mass calculator handles blocks, cylinders, pipes and spheres |
| Irregular solid | Water displacement: submerge it and measure the volume of water pushed aside |
| Object that floats | Displacement still works, but you must hold it fully under |
| Porous or absorbent | Displacement measures the outer volume including sealed pores, not the solid material |
| Powder or aggregate | You get bulk density, which includes the air between particles |
| Field | Why it matters |
|---|---|
| Construction | Dead load calculations start from material density — concrete at 2,400 kg/m³ adds up fast |
| Freight and logistics | Dense cargo hits weight limits; bulky cargo hits volume limits. Density decides which |
| Marine | Buoyancy, draught and stability all follow from density and displacement |
| Materials selection | Aluminium at 2,700 kg/m³ against steel at 7,850 is why aircraft use it |
| Quality control | Density is a quick check for purity, alloy composition or trapped air |
| Geology and soil | Compaction is measured as achieved density against a reference |
In Australian construction, density figures feed directly into structural calculations. A cubic metre of reinforced concrete at about 2,500 kg is 2.5 tonnes of dead load before anything is placed on it, which is why slab and beam design starts with the material's own weight.
How do you calculate density?
Divide mass by volume. A 2 kg object occupying 1 litre has a density of 2 kg per litre, which is 2,000 kg/m³. Keep the units consistent — mixing grams with cubic metres is the usual source of errors that are wrong by a factor of a thousand.
What is the density formula?
Density equals mass divided by volume, usually written ρ = m/V. Rearranged, mass is density times volume and volume is mass divided by density. The calculator above solves whichever one you select.
What is the SI unit of density?
Kilograms per cubic metre (kg/m³). Grams per cubic centimetre is also common and differs by exactly a factor of 1,000 — water is 1,000 kg/m³ or 1.0 g/cm³. Grams per millilitre is identical to g/cm³, since a millilitre is a cubic centimetre.
What is the density of water?
About 1,000 kg/m³, but not exactly, and it varies with temperature. Water peaks at roughly 999.97 kg/m³ near 4 °C and falls to about 998.2 kg/m³ at 20 °C. Sea water is denser at around 1,025 kg/m³ because of dissolved salts.
What is specific gravity?
Density expressed relative to fresh water, so it has no units. Steel's specific gravity is 7.85 because it is 7.85 times as dense as water. The useful part is the threshold: below 1.00 a material floats in fresh water, above 1.00 it sinks.
Why do objects float or sink?
An object floats if its average density is less than the fluid's. Archimedes' principle puts it another way — it floats when it displaces a weight of fluid equal to its own weight. What matters is the average density of the whole object, including any air it encloses, not the density of the material it is made from.
Why do steel ships float when steel sinks?
Because a hull encloses a large volume of air, the ship's average density — steel, air and cargo divided by total volume — is below that of water. A solid block of the same steel has nothing but steel in it and sinks. Flooding a hull raises its average density above water's, which is what sinking is.
Why does ice float?
Because water is unusual: it reaches maximum density at about 4 °C and becomes less dense as it cools further. Ice at 0 °C is around 917 kg/m³, roughly 8% lighter than liquid water. This is why lakes freeze from the surface down rather than solid from the bottom, and why water pipes split when they freeze.
Can density change?
Yes. Density falls as most materials warm and expand, and rises as they cool — water being the notable exception below 4 °C. Gases change dramatically with both temperature and pressure. Published densities normally assume around 20 °C at atmospheric pressure.
How do I measure the density of an irregular object?
Weigh it, then find its volume by water displacement — fill a container to the brim, submerge the object fully, and measure the overflow. The overflow volume equals the object's volume, and mass divided by that gives density. A measuring jug and kitchen scales are enough for a usable result.
What is the difference between density and bulk density?
Density refers to the solid material. Bulk density includes the air gaps in a loose material such as sand, gravel or grain, so it is always lower. When you buy a cubic metre of gravel you are buying bulk volume, and the bulk density is what determines its mass.
What is the difference between density and weight?
Density is mass per unit volume and does not depend on gravity — a material has the same density on the Moon as on Earth. Weight is the force gravity exerts, measured in newtons, and it does change with location. Our weight and force calculator covers that distinction.
Density is the simplest of relationships and the one most often mangled by units. A factor of a thousand between g/cm³ and kg/m³ accounts for most wrong answers, and keeping the units straight solves nearly everything else.
The specific gravity figure is worth glancing at whenever you calculate a density — it tells you instantly whether the material floats, and whether the number you just produced is plausible for what you were measuring.
To go from material and dimensions straight to mass, use the mass calculator. For converting an existing mass between units, the weight converter.