A light metal is any metal of relatively low density. These may be pure elements, but more commonly are metallic alloys. Lithium and then potassium are the two lightest metallic elements.

Magnesium, aluminium and titanium alloys are light metals of significant commercial importance. Their densities of 1.7, 2.7 and 4.5 g/cm³ range from 19 to 56% of the densities of other structural metals, such as iron (7.9) and copper (8.9).