Need to find the density of a rock, liquid, or any object? Just enter any two values — mass, volume, or density — and our free density calculator gives you the third instantly. Works with all units (grams, kilograms, liters, cubic centimeters). Perfect for science homework, lab work, or just satisfying your curiosity.
| Unit | kg/m³ |
|---|---|
| kilogram/cubic meter [kg/m³] | SI Unit |
| kilogram/cubic centimeter | 1,000,000 |
| gram/cubic meter [g/m³] | 0.001 |
| gram/cubic centimeter | 1,000 |
| kilogram/liter [kg/L] | 1,000 |
| gram/liter [g/L] | SI Unit |
| pound/cubic inch [lb/in³] | 27,680 |
| pound/cubic foot [lb/ft³] | 16.02 |
| pound/cubic yard [lb/yd³] | 0.593 |
| pound/gallon (US) | 119.83 |
| pound/gallon (UK) | 99.78 |
| ounce/cubic inch [oz/in³] | 1,730 |
| ounce/cubic foot [oz/ft³] | 1.001 |
| ounce/gallon (US) | 7.489 |
| ounce/gallon (UK) | 6.236 |
| ton (short)/cubic yard | 1,186.6 |
| ton (long)/cubic yard | 1,328.9 |
| psi/1000 feet | 2.307 |
Density (ρ) is defined as mass per unit volume: ρ = m / V. Density is affected by pressure and temperature. For solids and liquids, density changes are typically small. For gases, temperature and pressure significantly affect density.
Density is basically how "packed" something is. Think about it like this.
Imagine you have a suitcase. If you stuff it full of clothes, it's heavy and dense. If you just throw in one t-shirt, it's light and not very dense. Same suitcase. Different amount of stuff inside.
That's density. It's how much mass (the "stuff") is crammed into a certain amount of space (the volume).
density = mass / volume
That's it. That's the whole formula. Don't let anyone make it sound more complicated than it is.
Our calculator is super straightforward. You'll see three boxes: one for density, one for mass, and one for volume.
Pick what you want to find. Do you need density, mass, or volume?
Enter the two values you know. If you want density, put in the mass and volume.
Choose your units. Grams, kilograms, liters, cubic centimeters — pick whatever you're working with.
Hit calculate. That's it.
🪨 Real Example:
Rock weighs 150 grams. Volume is 50 cubic centimeters. Put 150 in mass, 50 in volume, hit calculate. Answer: 3 g/cm³. Easy.
ρ = m / V
ρ (rho) = density | m = mass | V = volume
But here's what most people get wrong. You need to make sure your units match. If mass is in grams, volume should be in cm³ or mL. If mass is in kilograms, volume should be in liters or m³. Mix them up and your answer will be way off.
Cover M
See D × V
mass = density × volume
Cover D
See M / V
density = mass / volume
Cover V
See M / D
volume = mass / density
Metal is denser than water, so shouldn't ships sink? But a ship is hollow inside. All that empty space makes its overall density less than water. Same material, different shape, different density. That's why a solid metal ball sinks but a metal boat floats.
When you heat air, it expands — same amount of air takes up more space, so density goes down. Hot air is less dense than cool air. That's why hot air balloons rise — like a bubble in water.
Water is weird. Most things get denser when they freeze. But water expands, making ice less dense than liquid water. If ice were denser, lakes would freeze from the bottom up and fish would die. Thank density for ice cubes.
Finding density is easy for regular shapes — just measure sides and calculate volume. But what about something weird like a rock or a key?
Why does this work? The object pushes water out of the way. The amount of water displaced equals its own volume. Then weigh it, divide mass by volume, and you've got density.
Mistake #1: Using the Wrong Units
If mass is in grams and volume is in liters, your answer will be wrong. Convert everything to the same unit system first. For most problems, use grams and cm³ (or mL).
Mistake #2: Forgetting to Convert
1 kg = 1000 g. 1 m³ = 1,000,000 cm³. Our calculator handles conversions, but if doing it by hand, double-check.
Mistake #3: Confusing Mass and Weight
Mass is how much stuff. Weight is gravity's pull. On Earth they're similar, but in space they're different. For density, always use mass.
Mistake #4: Not Accounting for Air Bubbles
When using water displacement, air bubbles stuck to your object make volume seem bigger than it really is — messing up your density calculation.
Rule of thumb: anything with density less than 1,000 kg/m³ (1 g/cm³) floats on water. Anything higher sinks. The extremes — from thin air to black holes — span an unimaginable range.
When you heat something up, it usually expands — same mass, more space, lower density. Cool it down, it contracts — density goes up. This is why hot air rises.
But water is weird again. Water is densest at 4°C (39°F). Below that, it starts expanding. That's why ice floats. If water behaved like everything else, ice would sink and life would be very different.
Gases have density too, but they're compressible so the formula gets trickier. For most practical purposes, density = mass / volume still works — just measure gas at a specific temperature and pressure.
At room temperature and normal pressure, air has a density of about 0.0012 g/cm³. That's why we don't notice it — it's super light.
Engineers use density to choose materials for buildings and bridges.
Chefs use density when cooking — different oils have different densities.
Geologists use density to identify rocks and minerals.
Doctors use density in bone density tests to check for osteoporosis.
Environmental scientists track oil spills because oil is less dense than water.
Neutron stars are the densest things in the universe. A single teaspoon of neutron star material would weigh about 10 million tons — the weight of a whole mountain in a spoon.
Compare that to gold at 19.32 g/cm³. A neutron star is about 100 trillion times denser. So next time you're calculating density, remember — it could always be weirder.
Use the water displacement method. Fill a graduated cylinder with water and note the level. Drop the object in and note the new level. Subtract to get volume. Weigh the object and divide mass by volume. That's your density.
Mass is how much "stuff" is in an object. Density is how tightly that stuff is packed. A brick and a sponge can have the same mass, but the brick is denser because all that mass is crammed into a smaller space.
Water is weird. When it freezes, it expands instead of contracting. That makes ice less dense than liquid water. So ice floats. Most other things get denser when they freeze and would sink.
Measure one side of the cube. Volume = side × side × side. Weigh the cube. Divide mass by volume. Make sure your units match.
For most problems, use grams per cubic centimeter (g/cm³) or grams per milliliter (g/mL) — they're the same. For bigger things, use kg/m³. Just make sure mass and volume units match.
Yes, but be careful. Gases are compressible, so density changes with temperature and pressure. The calculator works if you know mass and volume. For accurate gas density, use the ideal gas law.
Pure water = 1 g/cm³ at 4°C (39°F). That's the standard. Salt water is slightly denser at about 1.025 g/cm³ — that's why it's easier to float in the ocean than a pool.
To convert g/cm³ to kg/m³, multiply by 1000. So 1 g/cm³ = 1000 kg/m³. To go back, divide by 1000. Our calculator handles unit conversions automatically.