It only works if you grew up in a country that uses Fahrenheit. I didn’t, so to me Celsius is how I feel. I’ve no idea whether 20 f is jeans and a t-shirt weather, or if I should be getting my coat. 20 c however I know that as long as it’s not windy I’ll be good with jeans and a t-shirt, but that it’s still a little too cool to get out my shorts.