Sleeping Bag Temperature Translator
Converts between EN/ISO Comfort, Limit, and Extreme ratings — and explains what each band actually means.
Inputs
Result
A natural placement between the calculator and the explanation.
What this solves — and what it doesn't
Bag ratings are notoriously confusing because Comfort, Limit, and Extreme describe very different things. The EN/ISO 23537 standard rates: Comfort (a standard woman sleeps warm), Limit (a standard man sleeps curled-up but OK), and Extreme (a standard woman survives — not comfortable, possibly hypothermic). Most casual users buy to the Limit number and then freeze. This tool re-derives an effective comfort rating using your pad R-value and your sleep-warmth tendency.
How to read the result
The result is a ‘margin to comfort’ in C. Positive margin means you’ll sleep comfortably. Negative margin means you should add layers, a liner, or a warmer bag.
The ‘Effective comfort’ line applies two adjustments: ~3 C colder for cold-sleepers (and most women), ~1.5 C warmer per unit of pad R-value above 3.
The ‘survival-limit’ line is what the manufacturer would let you get away with — treat it as an emergency lower bound, not a planning target.
Limitations
- No humidity adjustment. Wet bags lose significant loft.
- Doesn’t model metabolism disorders or alcohol.
- EN/ISO 23537 assumes a standardized sleeping pad (R~4) — your pad matters more than the bag’s tag in many cases.
Frequently asked questions
Is the Extreme rating usable?
Rarely. EN/ISO Extreme represents survival, not sleep. Plan well above Extreme for any extended trip.
Why does pad R-value matter so much?
Because ground conduction is the largest heat loss for most sleepers. A good pad can make a marginal bag work in a pinch.
Should I size up to feel safer?
If you’re a cold sleeper, yes. If you’re warm, the calculator already adjusts.