四因子公式（英语：The four-factor formula）是由美国科学家费米所提出，应用于核工程核连锁反应无限增殖因数计算的公式。

此公式为：

The four-factor formula, also known as Fermi's four factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in an infinite medium. The formula is

The six factor formula defines each of these terms in much more detail.