Sleeping Bag Temperature Rating Calculator
Work backwards from the coldest night you expect: the calculator outputs the comfort and lower-limit ratings that keep the system in balance, plus the pad R-value that matches.
Result
- Required lower-limit rating
- 32.5 °F
- Recommended pad R-value
- R 4.5
How the calculation works
This page runs the warmth calculator backwards. Instead of asking "is my bag warm enough", it asks "what rating keeps the system in balance" for the night you described, with the same correction set: pad R-value (3 °C per point around the R-5 test pad), worn clothing (3 °C per clo, 3 clo cap), wind exposure scaled by shelter, altitude above 3,000 m and your sleeper type.
The lower-limit figure is simply the comfort figure shifted by the standard's roughly 5.5 °C offset, so a bag whose comfort rating matches will comfortably cover the same night for a cold-tolerant sleeper. The matching pad R-value is the rating the bottom of the system needs so it does not give the margin back.
Read the guide to EN/ISO temperature ratings for how those labels are tested, and the sleeping warm checklist for the habits that protect the rating you already own. A full check of an existing bag lives on the warmth calculator. For the other half of the fit question - whether a Regular cut even fits you - the sleeping bag size calculator turns your height into a length call.
Planning estimate only - not safety advice.
Frequently asked questions
Should I buy a bag for its comfort or lower-limit rating?
The comfort rating (ISO 23537 standard woman) is the honest planning number for most people; the lower limit (standard man) runs roughly 5-6 °C colder. Match the comfort rating to the coldest night you expect with a margin, and treat the lower limit as a survival estimate, not a sleep guarantee.
Why does the required rating get warmer when my pad is worse?
Because the bag has to cover the bottom-loss the pad does not. The EN test pad is R-5; on an R-2 pad the bag effectively performs about 9 °C worse than its label. The calculator shifts the required rating to compensate.
How much clothing can I credit in the bag?
The model credits 3 °C per clo up to 3 clo - about what a base layer, insulated jacket and beanie add up to. Beyond that, bulk compresses insulation and the credit stops being real. Clothing is also a rescue tool for cold nights, not the plan itself.
What temperature should I plan for?
The forecast low for the specific campsite, not the town. Valleys and basins can be 5-10 °C colder than the nearest forecast grid point on clear nights. Enter the number you actually expect at 2 a.m., then let the margin rule do its work.