How this calculator works
Hawking radiation assigns a temperature to a nonrotating, uncharged horizon. The temperature falls inversely with gravitational mass. This is the radiation temperature seen far from the black hole, not the temperature of nearby accreting gas. A surrounding radiation bath can deliver more energy than the hole emits. The formula uses CODATA 2022 constants and assumes the semiclassical regime, far above the Planck mass.
Formula
T_H = h c^3 / (16 pi^2 G k_B M) = hbar c^3 / (8 pi G k_B M).
Worked example
A black hole of mass 1e12 kg has temperature about 1.226900670594e11 K. Doubling its mass halves this temperature.
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Frequently asked questions
Does a larger black hole radiate at a higher temperature?
No. Hawking temperature is inversely proportional to mass.
Does this describe an accretion disk?
No. A luminous disk is heated by infalling material and can be much hotter than the horizon radiation.
Can I enter zero mass?
No. The inverse formula is singular at zero, and quantum-gravity effects matter long before that limit.