Free Tool
Sleeping Bag Temperature Calculator
Stop guessing which rating you need. Enter your conditions — sleeping style, pad warmth, shelter, and temperature — and get a personalized EN/ISO-calibrated recommendation.
EN/ISO bag ratings are calibrated to a female test subject (cold sleeper). Men typically run warmer and can use the limit rating — about 10°F above the comfort rating.
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What's shaping your rating
Comfort vs Limit Rating
Under the EN/ISO standard, the comfort rating is the lowest temp at which a cold-sleeping woman can sleep comfortably in a relaxed position. The limit rating is ~10°F warmer — the lowest temp a warm-sleeping man can survive curled up. Always buy to the comfort rating if you run cold or want margin.
Why Pad R-Value Matters
You lose up to 30% of body heat through direct ground contact. A thin foam sit pad (R-1) barely slows this. EN/ISO bag ratings assume a sleeping pad of roughly R-3 under the test subject. If your pad is thinner, your bag effectively performs warmer than rated — you need more insulation elsewhere.
The 10°F Safety Buffer
Most experienced backpackers buy a bag rated 10–15°F colder than their expected low. Forecasts are wrong, conditions change, and exhaustion affects how warm you sleep. A bag rated too warm means a sweaty, uncomfortable night — a bag rated too cold can be dangerous. This calculator already builds in some buffer; add more if you run cold.
Frequently Asked Questions
What temperature sleeping bag do I need?
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.
What is the difference between comfort and limit rating on sleeping bags?
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.
Does sleeping pad R-value affect sleeping bag warmth?
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.
Do men and women need different sleeping bag ratings?
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.
How does shelter type affect sleeping bag choice?
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.
Should I buy a sleeping bag exactly rated to my low temperature?
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.