The formulas
°F = °C × 1.8 + 32. K = °C + 273.15. Kelvin has no degree symbol because it's an absolute scale starting at absolute zero (−273.15 °C).
Anchors worth remembering
Water freezes at 0 °C / 32 °F, body temperature is about 37 °C / 98.6 °F, and −40 is the same in both scales — the classic trick-question crossover point.