Osmium is the most dense metal! Many people are familiar with lead (11.3 kg/L), but osmium is twice as dense (22.6 kg/L)! Each liter (about 1/4 gallon) of osmium weighs 22.6 kg (50 lbs). For comparison, each liter of water weighs only 1 kg (~2.2 lbs). Some other heavy metals include tungsten and gold (19.3 kg/L), which are almost as dense as osmium.