在电路学里，给定电势差，电容器保存电荷的能力，称为电容（capacitance），标记为C。采用国际单位制，电容的单位是法拉（farad），标记为F。电路图中多半以C开头标示电容，例如，C01、C02、C03、C100等。

平行板电容器是一种简单的电容器，是由互相平行、以空间或介电质隔离的两片薄板导体构成。假设这两片导板分别载有负电荷与正电荷，所载有的电荷量分别为、，两片导板之间的电势差为，则这电容器的电容为

1法拉等于1库仑每伏特，即电容为1法拉的电容器，在正常操作范围内，每增加1伏特的电势差可以多保存1库仑的电荷。

Capacitance is the ability of a body to store an electrical charge. A material with a large capacitance holds more electric charge at a given voltage, than one with low capacitance. Any object that can be electrically charged exhibits capacitance, however the concept is particularly important for understanding the operations of the capacitor, one of the three fundamental electronic components (along with resistors and inductors).