某个截面对于一个轴的面积矩，是指截面上一个微元面积与该微元距离该轴的距离的乘积的积分。它经常用来找出一个面积的重心。

其中：为微元距轴的距离

给定一任意形状之面积A，面积一次矩定义如下：

面积一次矩也会用表示。

The first moment of area, sometimes misnamed as the first moment of inertia, is based in the mathematical construct moments in metric spaces, stating that the moment of area equals the summation of area times distance to an axis [Σ(a × d)]. It is a measure of the distribution of the area of a shape in relation to an axis.