Interactive Tools
Black Hole Calculator: Size, Temperature & Lifetime
A free interactive black hole calculator. Set the mass and instantly see the Schwarzschild radius, the Hawking temperature, and how long the black hole would take to evaporate.
Last updated 23 May 2026 · How we research
Event horizon (diameter)
5.91 km
Hawking temperature
6.17 × 10⁻⁸ K
Time to evaporate
2.10 × 10⁶⁷ years
This black hole is colder than space itself (2.7 K), so today it absorbs more radiation than it emits and would not shrink. Its lifetime is far longer than the current age of the universe.
This calculator brings together three of the most striking numbers in physics. Set the mass of a black hole, from a person to a supermassive giant, and watch its size, temperature and lifetime change before your eyes.
The science behind the numbers
The Schwarzschild radius is the size of the event horizon: the point of no return. It grows in direct proportion to mass, so a black hole of twice the mass is twice as wide.
The Hawking temperature comes from Hawking radiation, Hawking's most famous discovery, and it is the quantity carved on his memorial stone. Crucially, it runs backwards to mass: the bigger the black hole, the colder it is. A black hole the mass of our Sun is far colder than empty space, which is why real black holes do not shrink today.
The evaporation time follows from that temperature. Because large black holes are so cold, they radiate incredibly slowly, and their lifetimes dwarf the current age of the universe. Only very small black holes evaporate quickly. This is also why Hawking radiation has never been directly observed, and why he never won a Nobel Prize.