在数学中，度量（度规）或距离函数是个函数，定义了集合内每一对元素之间的距离。带有度量的集合叫做度量空间。度量能导出集合上的拓扑，但不是所有拓扑都可以由度量生成。当一个拓扑空间的拓扑可以由度量来描述的时候，则称此一拓扑空间为可度量化的。

在微分几何中，“度量”一词也用来称呼定义为由微分流形的切矢量映射至纯量之双线性形式，让沿着曲线的距离可透过积分来取得。此一概念有个更适合的术语，称之为度量张量（或黎曼度量）。

In mathematics, a metric or distance function is a function that defines a distance between each pair of elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set, but not all topologies can be generated by a metric. A topological space whose topology can be described by a metric is called metrizable.