Iridium, with a calculated density of 22.65 grams per cubic centimeter, is the densest element, but osmium, with a density of 22.61 grams per cubic centimeter, is nearly identical. Density can vary depending on factors such as temperature and pressure. Under some conditions, osmium may appear denser than iridium.
Density is found by dividing the mass of a substance by the volume it occupies. Iridium and osmium are both roughly twice as dense as lead. Water is considered to have a relative density of 1, meaning substances with a relative density of less than 1 tend to float in water, while substances with a relative density greater than 1 tend to sink. Hydrogen, the most common element in the universe, is also the least dense, with a relative density of about 0.07 when compared to water.