Density Calculator

Three forms of one equation

Results are shown to six decimal places. Because units pass straight through, keep them consistent: if density is in g/cm³, mass must be in grams and volume in cm³. One milliliter equals one cubic centimeter, so lab and kitchen volumes in mL can be entered directly.

Density of common materials

These values come from the density table in OpenStax College Physics, given here in g/cm³ (multiply by 1,000 for kg/m³).

Gases are roughly a thousand times less dense than liquids and solids, which is why a cubic meter of air weighs about 1.3 kg while a cubic meter of water weighs 1,000 kg.

Unit conversions (U.S. and SI)

NIST Special Publication 811 gives the conversion factors to kg/m³:

Working the other way, 1 g/cm³ = 1,000 ÷ 16.01846 = 62.43 lb/ft³ and 1,000 ÷ 119.8264 = 8.345 lb/gal. That is where the familiar "a gallon of water weighs about 8.34 pounds" comes from. Gasoline at 0.68 g/cm³ works out to about 5.67 lb/gal.

Finding the volume of an irregular object

For a rock, a ring or a fishing weight, measure the volume by water displacement: fill a graduated cylinder or measuring cup partway, read the level, submerge the object fully and read again. The rise in milliliters is the object's volume in cm³. Weigh it on a kitchen or lab scale in grams, then divide. This is the method traditionally attributed to Archimedes for testing a gold crown, and it works for any object that doesn't absorb water or float.

For regular shapes, compute volume geometrically: a rectangular block is length × width × height; a cylinder is πr² × height.

Why water is "1" and when it isn't

The metric system was set up so water has a density of 1 g/cm³. USGS notes that water is densest at about 4 °C (39.2 °F) and that ice is roughly 9% less dense than liquid water, which is why ice floats and lakes freeze from the top down. Warm water is slightly less dense than cold, and seawater is denser than fresh water because of dissolved salt. For most calculations, 1.00 g/cm³ is accurate to within a fraction of a percent.

Specific gravity is the same idea without units: the ratio of a material's density to that of water. Aluminum has a specific gravity of 2.7, which means it is 2.7 times as dense as water.

Common mistakes

• Mixing g with kg or cm³ with m³. 1 m³ = 1,000,000 cm³, so a g/cm³ value entered against m³ is off by a factor of a million.
• Confusing weight and mass. In everyday U.S. use, pounds are treated as mass; for density this is fine, as long as volume is in matching units.
• Using nominal volume for porous materials. Wood, soil and powders contain air, so their bulk density is lower than the density of the solid material.
• Expecting "heavy" to mean "dense". A ship weighs thousands of tons, but its hull encloses so much air that its average density is below that of water, so it floats.

Will it float? Using density for buoyancy

An object floats in a fluid when its average density is lower than the fluid's, and the fraction that sits below the surface equals the ratio of the two densities. Ice at 0.917 g/cm³ in fresh water at 1.000 g/cm³ floats with about 92% of its volume submerged, which is where the "tip of the iceberg" idea comes from. Cork at 0.24 g/cm³ floats with only about a quarter submerged.

To use the calculator for this, compute the object's density first, then compare it with the fluid's value from the table above. For a mixture or a hollow object, use the total mass divided by the total outer volume; that average is what decides whether it floats. This is also how a hydrometer works: it sinks deeper in a less dense liquid and rides higher in a denser one, so the depth it settles at can be read as a density or specific gravity. Saltwater is denser than fresh water, so the same boat floats slightly higher in the ocean than in a lake.