I have no difficulty estimating sizes and weights in kilometers, meters and centimeters, in tons, kilograms or grams, or in assessing the weather in celsius.
0F, it's cold and the wind chill makes it miserable. 0C? That's 32F, which is technically freezing but I can still work on my cars outside in that weather.
100F, sweaty, hot, chugging water if you're outside. 100C? GG, you're dead.