斯特藩-玻尔兹曼常数（又称斯特藩常数），一个用希腊字母σ标记的物理常数，用于斯特藩-玻尔兹曼定律：黑体单位时间每单位面积的放射总能量与热力学温度的四次方成正比，其中的正比比率就是此常数。

σ的值为5.670 373(21)×10 W·m·K。本值既能被推导，亦能被实验测定；见斯特藩-玻尔兹曼定律

σ的定义能以玻尔兹曼常数表示：

其中h为普朗克常数，为狄拉克版的普朗克常数，而c则是真空中光速。

一个跟本常数有关系的常数放射常数()，其值等于

The Stefan–Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter σ (sigma), is the constant of proportionality in the Stefan–Boltzmann law: "the total intensity radiated over all wavelengths increases as the temperature increases", of a black body which is proportional to the fourth power of the thermodynamic temperature. The theory of thermal radiation lays down the theory of quantum mechanics, by using physics to relate to molecular, atomic and sub-atomic levels. Slovenian physicist Josef Stefan formulated the constant in 1879, and it was later derived in 1884 by Austrian physicist Ludwig Boltzmann. The equation can also be derived from Planck's Law, by integrating over all wavelengths at a given temperature, which will represent a small flat black body box. "The amount of thermal radiation emitted increases rapidly and the principal frequency of the radiation becomes higher with increasing temperatures". The Stefan-Boltzmann constant can be used to measure the amount of heat that is emitted by a blackbody, which absorbs all of the radiant energy that hits it, and will emit all the radiant energy. Furthermore, the Stefan–Boltzmann constant allows for temperature (K) to be converted to units for intensity (W⋅m), which is power per unit area.