Sleeping Bag Temp Rating Calculator
Match your sleeping bag's comfort and limit ratings to expected lows and sleeper type. Cold sleepers need +10°F buffer.
Quick Answer
Use the comfort rating, not the limit rating. Average sleeper: comfort rating ≤ expected low. Cold sleeper: comfort rating ≤ expected low minus 10°F. Warm sleeper: comfort rating ≤ expected low plus 5°F.
Recommendation
Buy a bag with a comfort rating at or below 32°F. The limit rating (20°F) is the discomfort threshold — you'll be cold but functional.
About This Tool
The Sleeping Bag Temp Rating Calculator translates expected nighttime temperatures into the comfort rating you should look for when buying a sleeping bag. Sleeping bag ratings are surprisingly confusing because manufacturers print three numbers (comfort, limit, extreme) and most people use them wrong. Using the limit rating instead of the comfort rating is one of the top reasons hikers wake up shivering.
Understanding EN/ISO Sleeping Bag Ratings
Modern sleeping bags use the EN 13537 / ISO 23537 standard, which specifies four temperature ratings derived from heated mannequin tests. The Comfort rating is the temperature at which a typical woman in a relaxed sleeping position can sleep without feeling cold. The Limit rating is the temperature at which a typical man curled up in the bag can just barely sleep without shivering. The Extreme rating is a survival temperature where hypothermia is possible but death isn't imminent within 6 hours. The fourth, Upper Limit, is when you start sweating.
Use the Comfort Rating, Not the Limit
The most common mistake: buying a bag whose limit rating matches the expected low. A bag with a 20°F limit rating has a comfort rating around 30-32°F. If you take it on a 25°F night, you'll be cold. Always shop by comfort rating, not limit. Marketing often emphasizes the lower (limit) number because it sounds more impressive — but it's the wrong number to plan around.
Sleeper Type Adjustments
People metabolize differently. About 20-30% of hikers sleep cold (always reaching for extra layers). About 20% sleep hot (kicking off blankets). The rest are average. Cold sleepers need 10°F more rating than the expected low — for 30°F nights, get a 20°F comfort-rated bag. Warm sleepers can run their bag closer to the comfort number. Hormones, hydration, exhaustion, and recent food all affect cold tolerance, so build in margin.
Down vs. Synthetic Insulation
Down (goose or duck plumage) has the highest warmth-to-weight ratio of any insulation. Premium 850-fill down bags weigh 30-40% less than synthetic bags at the same temperature rating. The downside: traditional down loses 50%+ of its insulation when wet. Treated/hydrophobic down (DownTek, NikWax) recovers most of that performance. Synthetic insulation (Climashield, PrimaLoft) is heavier but reliable when wet. For dry/cold conditions: down. For wet conditions or beginners: synthetic.
Pad R-Value Is Half the Equation
Your sleeping pad insulates you from the ground. R-value measures thermal resistance: R-1 is summer-only, R-3 is 3-season, R-5 is winter, R-7+ is expedition. A premium 0°F sleeping bag on an R-2 pad will leave you cold because the ground steals heat through your back. Pad R-values stack: a foam pad (R-2) plus an inflatable pad (R-3) gives you R-5. For trips below 30°F, get a pad rated R-4 or higher.
Liners and Layers Extend Range
A silk liner adds 5-8°F of warmth and keeps your bag clean. A fleece liner adds 8-12°F. Wearing a base layer, hat, and dry socks inside the bag adds 5-15°F more. These tricks can extend a 30°F bag down to 15°F for occasional cold snaps. Don't buy a 0°F bag for one annual winter trip if you can stretch your 20°F bag with a liner.
Plan Your Whole Sleep System
Pair this with our tent capacity calculator, our backpack weight calculator, and our altitude sickness risk tool. For trip planning, use our hiking time calculator.