| bgcolour = {default} | name = 密度 | image = | caption = | unit = kg/m | symbols = ρ
D | derivations = }->

密度是指一物质单位体积下的质量，常用希腊字母ρ或是英文本母D表示。在数学上，密度定义为质量除以体积的商：

其中ρ为密度，m为质量，V为体积。

有时（例如美国的石油业或天然气产业）会将密度定义为单位体积的重量，不过在科学上是不精确的，此物理量应称为重率。

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume: