It's an important point that multiplying and dividing temperatures in F or C makes no sense. Some people are somehow assuming half way from freezing which is arbitrary. Would a F user assume it means half way from 32F or 0F?
Halfway from 0°C, the freezing point of water.
Freezing (0C). Halfway through the liquid phase of water. Seems like an at-least-somewhat reasonable starting point.
It also depends on the altitude. At a high enough altitude it would be boiling.