Sleeping Bag Temperature Table
| Bag class | Comfort | Typical limit | Pad R you need |
|---|---|---|---|
| Summer | +10°C and above | +5°C | 2-3 |
| Warm 3-season | +5 to +10°C | 0°C | 3 |
| Standard 3-season | 0 to -5°C | -10°C | 3-4 |
| Winter | -10°C and below | -20°C | 5+ |
| Expedition | -20°C and below | -30°C | 5+ and vapor barrier |
A sleeping bag's temperature number is not the temperature you'll be comfortable at - it is one of three lines drawn through a standardized mannequin's night, and choosing by the wrong line is why people freeze in bags rated for the weather they camped in.
Bottom line: buy and sleep by the comfort rating, treat the lower limit as the survival-with-all-layers edge, and ignore the extreme number entirely - it is a six-hour survival figure, not a night's sleep. Summer bags start near +10 C comfort, three-season bags run 0 to -5 C, true winter bags live at -10 C and below.
The honest part: the rating assumes a sleeping pad underneath, and the ground steals more heat than the air does - a -10 C bag over a thin summer pad delivers a -2 C night at best. EN 13537 (now ISO 23537) tests bag on pad together; your under-insulation is half the system, and it is the half people buy last.
How to use
- Find the night's low on the table, then choose a bag whose comfort rating sits at or below that number - not its limit, not its extreme: comfort is the temperature a standard sleeper sleeps through undisturbed.
- Check the pad line in the table: each rating class assumes a minimum pad insulation (R-value), and pairing a -10 C bag with a 2-R summer pad voids the arithmetic - upgrade the pad before upgrading the bag.
- Dress the system: dry base layers, a hat, and a hot-water bottle at the core stretch a bag one class colder; wearing tomorrow's clothes inside the bag compresses loft and lies to you about the rating.
Frequently asked questions
What does the temperature on a sleeping bag actually mean?
Under EN 13537 / ISO 23537, bags carry three numbers: the comfort rating (a standard woman sleeps eight hours undisturbed), the lower limit (a standard man sleeps eight hours curled), and the extreme (survival for six hours - no sleep, no guarantee). The labels on budget bags sometimes cite old or self-set scales, which is why the table groups bags by season class with typical comfort ranges instead of trusting any single sticker number.
What is a 3-season sleeping bag?
A bag whose comfort rating lands roughly 0 to -5 C (upper-20s to low-20s F) - warm enough for spring through autumn nights at most elevations, too warm and too heavy for high summer at low altitude. It is the default first-bag recommendation because it covers the widest honest window; a summer bag (+10 C comfort) and a winter bag (-10 C and below) bracket it.
Why am I still cold in a bag rated warmer than the night?
Two usual culprits, in order: the pad underneath (ratings assume adequate ground insulation, and cold ground pulls heat faster than cold air), and moisture - a bag slept in damp, or in clothes sweated through on the hike in, loses loft and with it the still-air layer that does the insulating. Dry socks and a dry bag liner restore more warmth than another base layer.
Can I zip two sleeping bags together?
Only if both are right-zip and left-zip versions of compatible lines - then yes, it makes a double bag, with one honest caveat: two bodies each add humidity, and the combined bag's effective rating drops a class if either sleeper runs cold. For couples who camp apart sometimes, buying the zip-pair versions beats improvising two mismatched zips that were never tested together.