🛌 Sleeping Bag Temperature Guide
Sleeping bag numbers only help if you know which number to trust. Enter the coldest night you expect and how you sleep, and this guide tells you how low the bag's Comfort rating should go — all from the EN 13537 / ISO 23537 standard.
🛌 Recommended bag rating
Shop against the Comfort rating so a chilly night still lets you sleep.
Comfort rating of roughly −1 to −7 °C. Spring, summer, and autumn in most temperate places — the do-it-all bag.
The three EN 13537 / ISO 23537 ratings
| Rating | Who it's for | What it means |
|---|---|---|
| Comfort | Standard woman (25 y, 60 kg, 160 cm) | Can sleep comfortably in a relaxed position. The figure most people should shop against. |
| Limit | Standard man (25 y, 70 kg, 173 cm) | Can sleep eight hours curled up on the boundary of feeling cold. A boundary, not a target: plan on the Comfort rating. |
| Extreme | Standard woman, survival only | About six hours before hypothermia sets in, with a risk of frostbite. Never a planning figure. |
Season reference (by Comfort rating)
| Season | Comfort range | Typical use |
|---|---|---|
| Summer (1-season) | +2 °C and warmer | Comfort rating of about +2 °C and above. Warm lowland nights, huts, and festivals — light and packable. |
| 3-season | -7 °C to +2 °C | Comfort rating of roughly −1 to −7 °C. Spring, summer, and autumn in most temperate places — the do-it-all bag. |
| Winter (4-season) | -7 °C and colder | Comfort rating below about −7 °C. Frost, snow, and alpine cold — more insulation and more weight. |
The Extreme rating is a survival figure only — never plan a trip around it. A sleeping pad with enough R-value is just as important as the bag: cold ground steals warmth no bag can replace.
A rating is a starting point, not a promise
The EN/ISO test standardised sleeping bags so two brands' numbers finally mean the same thing — a real win for shoppers. But it is measured on a heated mannequin in still air, not on a tired, dehydrated human at the end of a long day. Buy a little warmer than you think you need and you can always vent a zip.
Pair the bag with a pad that has enough R-value for the ground, add a liner for a few extra degrees, and keep your insulation dry. Those three habits matter more than chasing the last degree on a spec sheet.
Cold nights cause hypothermia, so plan them with care. Check the forecast for where you will sleep, not the nearest town, the day before you go; tell someone where you are going and when you will be back; and never run a stove, heater, lantern or charcoal that burns fuel inside a tent or a closed vestibule: it gives off carbon monoxide, which you cannot see or smell. Shivering you cannot stop, fumbling hands, confusion or slurred speech are signs of hypothermia: get the person dry, insulated and warm, and get help.
❓ Frequently Asked Questions
What do the Comfort, Limit, and Extreme ratings mean?
They are the three temperatures reported under EN 13537 (now ISO 23537), measured on a heated mannequin. Comfort is the lowest temperature a 'standard woman' can sleep comfortably and relaxed. Limit is the lowest a 'standard man' can sleep for eight hours curled up on the edge of feeling cold. Extreme is a survival-only figure — about six hours before hypothermia, with frostbite risk — and should never be used to plan a trip.
Should I use the Comfort or the Limit rating?
Shop against the Comfort rating, whoever you are. The Limit is the lowest temperature a 'standard man' can sleep curled up on the edge of feeling cold: a boundary, not a target, so a bag read at its Limit is too cold for a night at that temperature. Warm sleepers can match the Comfort rating to the forecast low; cold sleepers (many women) should aim about 5 °C lower, and a windy, damp or exposed camp adds about 3 °C more (both rules of thumb). The Extreme rating is a survival figure and never a target.
How do seasons map to ratings?
As a rough guide, a summer (1-season) bag has a Comfort rating around +2 °C and above, a 3-season bag sits at roughly −1 to −7 °C, and a winter (4-season) bag is rated below about −7 °C. A single good 3-season bag covers spring, summer, and autumn for most temperate-climate campers.
Why does the pad matter as much as the bag?
A sleeping bag can only trap the warmth you produce; it cannot stop the cold ground from conducting heat straight out of your body. That job belongs to the sleeping pad and its R-value. A warm bag on a thin summer pad will still leave you cold, so match the pad's R-value to the conditions alongside the bag's rating.
What else makes a bag warmer or colder in the field?
Real-world warmth depends on far more than the label — a full stomach and dry base layers help, while damp insulation, wind, high altitude, tiredness, and dehydration all rob heat. A bag liner adds several degrees, and a well-fitted hood and draft collar keep warmth from escaping. Treat the rating as a starting point, not a promise.