Outdoor Calculators
Sleeping bag rating.
Enter the coldest overnight temperature you expect and your bag's rating. The checker compares the right rating for how you sleep, applies a safety margin and tells you what rating to buy. Runs in your browser; nothing is sent or stored.
Night and bag
Result
Fill the form and press Calculate.
Worked example
The forecast low is -5 C and your bag has a Limit rating of -7 C. You sleep average. The margin is -5 - (-7) = 2 C, which is under the 3 C safety margin, so the verdict is marginal. To meet the margin, shop for a bag rated -8 C or lower. If you sleep cold, the bag is treated as Comfort -2 C and the same night is too cold.
How it works
Sleeping bags tested to EN 13537 (now ISO 23537) have up to three ratings, measured on a heated manikin: Comfort is the lowest temperature at which a standard woman sleeps comfortably in a relaxed position; Limit is the lowest at which a standard man sleeps for eight hours curled up without waking from cold; Extreme is a survival rating for a woman for six hours with a risk of hypothermia. Never plan around Extreme.
The checker compares the expected low with Comfort for cold sleepers and most women, and with Limit for others. A bag with one unlabelled "temperature rating" is usually closer to Limit. If only the Limit is known and you sleep cold, Comfort is estimated as Limit + 5 C (real gaps on EN-rated bags are about 5 to 8 C). The safety margin covers forecast error, wind, damp and a thin pad. A liner or pad helps but is not counted. Cold exposure can be dangerous: not medical advice.
Sources and basis: EN 13537:2012 and ISO 23537-1:2022 (sleeping bag temperature test and Comfort, Limit and Extreme definitions). The 5 C Comfort offset and the 3 C default margin are planning figures. Checked 2026-10-05. Planning guide only, not medical or safety advice. Conditions, health and equipment change real needs; use your own judgment and local guidance.
FAQ
What do Comfort, Limit and Extreme mean?
Comfort is the lowest temperature a standard woman sleeps comfortably, Limit is the lowest a standard man sleeps for eight hours curled up, and Extreme is a survival-only rating for a woman with a risk of hypothermia.
Which sleeping bag rating should I use?
Use Comfort if you sleep cold or are a woman, and Limit if you are an average or warm sleeper. Do not plan around Extreme.
Why is there a safety margin?
Forecasts miss, valleys and lakeshores run colder, damp and wind lower the effective warmth, and a thin pad lets heat escape. A few degrees of margin is cheap insurance.
Does my sleeping pad matter?
Yes. Ratings are tested with the bag on an insulating mat. In cold weather use a pad with an R-value of 4 or more.
What if my bag only gives one rating?
Many non-EN bags show one number, usually closer to the Limit. Choose Limit in the form, and be conservative.