VERY generally speaking, 20s are warm, 30s are hot. Humidity changes this a lot. And yes, personal sensitivity to heat plays a role. I live in a dry climate, and I feel rather comfortable until we're close to 30 ºC. I remember reading something like the ideal room temperature for humans was around 20-22 ºC.

For those using F, this is, more or less, the scale of C:

Below 0: freezing (0 ºC being the freezing point of water, duh!)
0 to 10: cold (don't go out without a coat)
10s: cool (a sweatshirt or light coat may do)
20s: warm
30s: hot
40s: uncomfortably hot (stay in the shade and hydrate)
50s: you're dead (or you wish you were. Unsafe for humans)

[–] Eufalconimorph@discuss.tchncs.de 1 points 1 year ago* (last edited 1 year ago)

Eh, as a weirdo who uses Celsius a lot but lives in Buffalo, NY...

-20s is cold. Coat, gloves, scarf, & hat. Long underwear. Not too much evaporation from the lake since it can freeze, so not much snow.
-10s is chilly. Coat, probably zip it up towards the lower end of the range. Decent chance of apocalyptic snow.
0-10s is cool. Wear a sweater.
10s is nice. Maybe consider long sleeves & pants if it gets a bit cooler.
20s is shorts & t-shirt weather.
30s is all AC, all the time. Uncomfortably hot not too far into the range.
40s is "the humidity is now so high the air is soup, filled with mosquitoes".