Out of the box, your iPhone’s default Weather app supports both Celsius and Fahrenheit for depicting how hot or cold it is outside. While these might be two of the most popular units of measure concerning temperature, they’re certainly not the only ones.
Another unit that you don’t see very often unless you dabble in the world of science is Kelvin, and a free jailbreak tweak called 4000 Degrees Kelvin by iOS developer Sniper_GER unlocks this temperature unit throughout iOS.