First, you need to know where and when your story is set in, to know the temperature. It can go from 0 to -15°C (23 to 5°F), which is an average winter day in Canada btw, or -30 to -40°C (-22 to -40°F), which is pretty cold. If you go colder than that, I don’t know if you’re trying to kill your characters or something, but it’s really not a good idea.
When you have an idea how cold it is, you can continue:
Average cold, but not freezing in two minutes (around -5 at -15°C)
- if your character is in average clothing (long pants, long-sleeved shirt, etc.) they will be fine for about 30 to 60 minutes. Their limbs will not necessarily be hurting
- if they are in clothing suited for hotter situations (dress, skirt, shorts, short-sleeved shirt, etc.) I give them thirty minutes, if not less, before their limbs start hurting. Trust me, I know.
- if they have winter gear (snow pants, mittens, scarf, etc.) they can last multiple hours, if not a whole day
A bit freezing (around -20 at -30 °C)
- if your character is in average clothing (long pants, long-sleeved shirt, etc.) they will last 15 minutes at best before having consequences (intense shivering, limbs hurting, etc.) (This is very precise, so I might be a bit off, since I haven’t actually tested it)
- if they are in clothing suited for hotter situations (dress, skirt, shorts, short-sleeved shirt, etc.), it will start hurting like hell in 30 minutes tops (or less). Also, when the character steps ouside, they will feel the cold on their flesh, and it will be cold.
- if they have winter gear (snow pants, mittens, scarf, etc.) they could survive a day outside, maybe. They’ll start feeling pretty cold in a few hours.
Hell but make it cold ( -30 to -40°C)
- if your character is in average clothing (long pants, long-sleeved shirt, etc.) they are so screwed. No, I’m serious 1 hour, maybe less, and they will have hypothermia
- if they are in clothing suited for hotter situations (dress, skirt, shorts, short-sleeved shirt, etc.) I am so, so sorry for them. I don’t know when the hypothermia will kick in, but it won’t take long. At first, they will be fine, for five seconds or so. I’m not sure when their limbs will hurt, but it won’t take more than very few minutes
- if they have winter gear (snow pants, mittens, scarf, etc.) I don’t remember exactly, but it will take 3 hours, or a few more, before the cold is unbearable, if their face isn’t screaming in agony before that
- if there’s wind (probably) their eyes will tear, especially if there’s a lot of wind
- if your character is trying to protect themselves from the wind, they absolutely need something to protect themselves from the wind (a cave, or even a whole they dug in the snow)
- if there’s snow, ice, whatever, building a fire on top of it won’t be very useful, since it won’t last very long, and the warmth provided won’t be that much
- if they enter a warm place (a shelter, house, etc.) your character will probably feel like they’re burning, and their limbs will be very sitff, especially if they were out for a long time or in a very cold weather
- cold is tiring. it takes a toll on your body, who tries to keep its warmth
- your limbs will hurt at some point, starting by the extremities (feet, hands, head) except if they are covered (even though, for example, let’s say the character has good snow boots, but is wearing jeans, which are not much good against the cold, their legs will start freezing first, although their feet might stay okay for a bit)
- clothes get cold before your skin does, so if you enter a warm place, you’ll heat up, though your clothes will slow down the process (they can stay cold for a while), so I recommend your character changes clothes, maybe take a hot shower. Jeans are the clothes that keep cold in the most.
- hypothermia: Hypothermia is a medical emergency that occurs when your body loses heat faster than it can produce heat, causing a dangerously low body temperature. Normal body temperature is around 98.6 F (37 C). Hypothermia (hi-poe-THUR-me-uh) occurs as your body temperature falls below 95 F (35 C).
- I once have hypothermia, it was around -20/-25 C, I was in a school uniform (skirt, knee-length socks, long jacket, hat, good boots) and I waited for the school bus for about 1 hour and 30 minutes. In the bus, I kept my jacket tightly around me for all the twenty minutes of the ride. At school, where there was way more heat than in the bus, I kept shaking (my legs especially) around 1 hour to 2 hours. My teeth chattered as well, in irregular intervals and stopped randomly. I was still cold for at least 30 minutes after entering the building, even if my friends told me my body had heat up since my entrance.
- your character can forget that they are cold if they are distracted (it won’t take it all away, and they won’t magically warm up, but they won’t be thinking about it). Though the colder and longer it gets, the harder it will be for them to get distracted
- hands stay cold for a long time and are the most efficient way to know if someone is cold, or was in the cold (and I’m not talking abouut people who have cold hands naturally)
That’s all I have for the moment, feel free to add more:)