Density Calculator

What Is Density?

Density is the mass of a substance per unit of volume. A block of lead and a block of wood of the same size take up the same space, but the lead holds at least 12 times more mass, so it is denser. The symbol is the Greek letter ρ (rho), and the SI unit is the kilogram per cubic meter (kg/m³). Chemistry and school labs usually use grams per cubic centimeter (g/cm³), which is the same as grams per milliliter (g/mL), while US engineering uses pounds per cubic foot (lb/ft³).

This density calculator solves the formula in any direction: mass and volume give density, density and volume give mass, and density and mass give volume. It converts every unit to kilograms and cubic meters first, then reports the answer in your unit with the specific gravity, the closest of 32 reference materials and a float or sink check for fresh water and seawater.

Density depends on the material, not the sample size: a paper clip and a steel beam are both about 7.8 g/cm³. It changes with temperature and pressure, strongly for gases, so reference values state their conditions.

Density Formula: How to Calculate Density, Mass or Volume

Know any two of the three quantities and the formula gives the third. In the triangle m over ρ × V, cover the one you want to see the operation.

How to calculate density manually

1. Measure the mass. Weigh the object on a scale and note the unit, for example 500 g.
2. Measure the volume. Use a ruler for a regular shape or water displacement for an irregular one, for example 185 cm³.
3. Match the units. Grams pair with cubic centimeters to give g/cm³; kilograms pair with cubic meters to give kg/m³.
4. Divide mass by volume. 500 ÷ 185 = 2.7027, so the density is 2.703 g/cm³ to four significant figures.
5. Convert if needed. Multiply g/cm³ by 1,000 for kg/m³ (2,702.7 kg/m³) or divide kg/m³ by 16.0185 for lb/ft³ (168.7 lb/ft³).

To find mass from density, multiply the density by the volume in matching units. To find volume from density, divide the mass by the density. Ethanol at 0.791 g/cm³ shows the second case: 100 g of it fills 100 ÷ 0.791 = 126.4 mL, more than 100 mL, because ethanol is less dense than water.

How to Find the Density of an Irregular Object

A rock or a ring has no simple volume formula, so use the water displacement method: a fully submerged object pushes aside exactly its own volume of water.

1. Weigh the dry object, for example 250 g.
2. Fill a graduated cylinder partway and read the bottom of the curved surface, for example 50 mL.
3. Tilt the cylinder and slide the object in so no water splashes out, then read the new level, for example 80 mL.
4. Subtract: 80 − 50 = 30 mL, which is 30 cm³.
5. Divide: 250 g ÷ 30 cm³ = 8.333 g/cm³, close to brass at 8.44 g/cm³.

A second method weighs the object twice, once in air and once hanging fully under water. By Archimedes' principle the buoyant force equals the weight of the water displaced, so the apparent mass loss equals the mass of that water. OpenStax works this for an ancient coin: 8.630 g in air and 7.800 g in water give a loss of 0.830 g, a volume of 0.830 cm³ and a density of 8.630 ÷ 0.830 = 10.40 g/cm³, close to silver at 10.49 g/cm³.

Density of Water by Temperature

The density of water is 0.99997 g/cm³ at 4 °C, its densest point, and 0.99820 g/cm³ at 20 °C. Water expands as it warms, so a gallon of hot water weighs less. Densities are USGS values; the US columns are computed with the exact NIST factors.

The USGS rounds the 4 °C value to 1.00000; the more precise figure is 0.99997 g/cm³. How much does a gallon of water weigh? About 8.33 lb at room temperature: 3.785411784 L × 0.99820 kg/L = 3.7786 kg, and 3.7786 ÷ 0.45359237 = 8.330 lb. Seawater averages about 1.025 g/cm³, so a gallon of it weighs about 8.554 lb.

Why ice floats

Freezing water forms an open crystal lattice, so ice at 0 °C has a density of about 0.917 g/cm³, around 8 percent less than liquid water at 20 °C. Ice floats with 0.917 ÷ 0.99984 = 91.7 percent of its volume under fresh water near 0 °C, and an iceberg floats with 0.917 ÷ 1.025 = 89.5 percent under seawater.

Density Unit Conversions

Each density unit is a mass unit over a volume unit, so every factor follows from the exact definitions 1 lb = 0.45359237 kg, 1 in = 2.54 cm and 1 US gallon = 231 in³. The calculator converts inputs to kg/m³ and converts the answer back.

Specific Gravity and Will It Float?

Specific gravity (relative density) is a density divided by the density of water. It has no units, and it equals the density in g/cm³ to within 0.003 percent when the reference is water at 4 °C, the reference this calculator uses. Aluminum at 2.70 g/cm³ has a specific gravity of 2.700.

An object floats when its average density is below the fluid's, sinks when it is above and hovers when they match. The calculator checks fresh water at 20 °C (0.9982 g/cm³) and seawater (1.025 g/cm³); a material between the two sinks in a lake but floats in the ocean.

For an object that sinks, the calculator reports its weight in water: aluminum at 2.7027 g/cm³ keeps 1 − 0.9982 ÷ 2.7027 = 63.07 percent of its dry weight. A steel ship floats because its hull encloses air, which lowers its average density.

Density vs Mass vs Weight, and the Density of Air

Mass is the amount of matter, in kilograms or pounds. Weight is the force of gravity on that mass, in newtons; on Earth 1 kg weighs about 9.81 N. Density is mass divided by volume, so a ton of feathers and a ton of bricks share a mass but not a density.

NASA gives dry air a density of 1.293 kg/m³ at 273 K and 101.325 kPa. The ideal gas law gives the value at room temperature:

Helium at 0.18 kg/m³ is lighter than air, so a helium balloon rises, while carbon dioxide at 1.98 kg/m³ is heavier and collects near the floor.

Density of Common Materials

The chart in the results lists 32 substances from hydrogen to osmium. The density of aluminum is 2.70 g/cm³, the density of steel is about 7.8 g/cm³ and pure iron is 7.87 g/cm³. Copper is 8.96 g/cm³, lead 11.3 g/cm³ and the density of gold is 19.32 g/cm³, which is 2.45 times iron, while iron is 2.91 times aluminum.

Osmium, at 22.59 g/cm³, is the densest element at room temperature and about twice as dense as lead, so the calculator flags any result above it as a likely unit mistake. Tungsten, at 19.30 g/cm³, is so close to gold that density alone cannot verify a gold bar.

Liquids and natural materials vary more. Gasoline runs from 0.66 to 0.69 g/cm³, so a gallon weighs 5.51 to 5.76 lb, and dry wood ranges from 0.3 to 0.9 g/cm³ by species.

Frequently Asked Questions

Sources & References

• National Institute of Standards and Technology. NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement (exact pound, inch and gallon). nist.gov
• National Institute of Standards and Technology. NIST Guide to the SI (SP 811), Appendix B.8: Factors for Units Listed Alphabetically (density factors, imperial gallon). nist.gov
• U.S. Geological Survey, Water Science School. Water Density (water from 0 to 100 °C, ice, hydrometers). usgs.gov
• U.S. Geological Survey, Water Science School. Facts About Water (8.33 pounds per gallon). usgs.gov
• NOAA National Centers for Environmental Information. World Ocean Database 2018 notes (seawater density of 1025 kg/m³). noaa.gov
• OpenStax. College Physics 2e, Section 11.2 Density, Table 11.1 (densities of solids, liquids and gases). openstax.org
• OpenStax. College Physics 2e, Section 11.7 Archimedes' Principle (buoyancy, specific gravity, coin example). openstax.org
• Royal Society of Chemistry. Periodic Table (Al, Fe, Cu, Au, Pb and Os densities; osmium 22.5872 g/cm³). rsc.org
• Simon Fraser University, Department of Physics. Density of Common Fluids (water at 4 and 20 °C and liquids at 20 °C, from the CRC Handbook). sfu.ca
• NASA Earthdata. Air Mass/Density (dry air 1.293 kg/m³ at 273 K and 101.325 kPa). nasa.gov

Results are estimates for educational use. Every number on this page was recomputed with the same formulas and conversion factors the calculator uses. Reference data reviewed: 2026.