Celsius, Fahrenheit and Kelvin — pick any two directions and type.
Formulas: °F = °C × 9/5 + 32; K = °C + 273.15. Every conversion routes through Celsius so all three scales stay consistent.
Where do Celsius and Fahrenheit meet? At −40: −40 °C and −40 °F are the same temperature.
What is absolute zero? 0 Kelvin = −273.15 °C = −459.67 °F — the lowest possible temperature.