轻子数是粒子物理学中定义的一个量子数，常用L来表示。轻子数规定为轻子的数目减去反轻子的数目。方程形式：

因此所有的轻子的轻子数为+1, 反轻子的轻子数为−1, 非轻子粒子的轻子数为0. 轻子数(有时也称作轻荷)是可加的量子数, 这意味着它的和在作用下守恒(与之相反的是可乘的量子数如宇称, 它的积在电磁作用与强相互作用下是守恒的).

类似于轻子数, 各轻子族数的定义

与轻子数的定义有相同的模式: 该族粒子的该量子数为+1, 该族反粒子的该量子数为−1, 非该族的粒子的该量子数为0.

In particle physics, the lepton number is a conserved quantum number representing the number of leptons minus the number of antileptons in an elementary particle reaction.

In equation form,

so all leptons have assigned a value of +1, antileptons −1, and non-leptonic particles 0. Lepton number (sometimes also called lepton charge) is an additive quantum number, which means that its sum is preserved in interactions (as opposed to multiplicative quantum numbers such as parity, where the product is preserved instead).