Sleeping Bag Temperature Calculator

Buy a bag rated 10–15°F colder than your expected overnight low. If your low is 30°F, target a 15–20°F rated bag. Adjust for whether you sleep cold or warm, your pad's R-value, and your shelter type — all of which affect how cold you actually feel.

Under the EN/ISO standard, the comfort rating is the lowest temperature at which a cold-sleeping woman can sleep comfortably in a relaxed position. The limit rating is approximately 10°F warmer, the lowest temperature at which a warm-sleeping man can sleep curled up. Always buy to the comfort rating if you run cold or want safety margin.

Yes. You lose up to 30% of your body heat through direct ground contact. EN/ISO sleeping bag ratings are tested with approximately an R-3 pad underneath. If your pad has a lower R-value, you need a warmer-rated bag to compensate. Each R-1 difference roughly equals 7°F of effective warmth.

Yes. EN/ISO bag ratings are calibrated to a female test subject (a cold sleeper). Men typically sleep about 10°F warmer and can comfortably use the limit rating rather than the comfort rating. This calculator adjusts for this automatically.

A 3-season tent adds roughly 5–10°F of warmth compared to sleeping in the open, because it blocks wind and retains some body heat. A bivy adds 8–10°F. A hammock, however, loses significantly more heat from below and may require a warmer bag or underquilt.

No. Always buy with margin — at least 10°F colder than your expected low. Weather forecasts are imperfect, altitude affects temperature more than expected, and fatigue makes you sleep colder. A bag rated too warm just means an uncomfortable night; a bag too cold in serious conditions can be dangerous.