what temperature for… · outdoors
You asked
What temperature rating do you need for a sleeping bag?
Pick a bag rated 10–15°F LOWER than the coldest night you expect: a 20°F bag for typical 3-season camping, 30°F+ for summer, under 15°F for winter. Use the ISO "comfort" rating if you sleep cold — the advertised number on unisex bags is usually the survival-leaning "lower limit."
The full answer
The two numbers on the tag (ISO 23537)
Since the EN 13537 / ISO 23537 lab standard, most reputable sleeping bags carry standardized ratings measured with a heated manikin:
| Rating | What it means | Who should use it |
|---|---|---|
| Comfort | A "cold sleeper" rests comfortably, relaxed posture | Women's bags are usually labeled with this; cold sleepers of any sex should shop by it |
| Lower limit | A "warm sleeper" can sleep curled without waking from cold | The number usually advertised on men's/unisex bags |
| Extreme | Survival-only: six hours without hypothermia death, frostbite possible | Never a shopping number |
The trap: a "20°F bag" (lower limit) has a comfort rating around 30–32°F. Two people in "20-degree bags" can have genuinely different nights at 25°F — one of them was sold a survival-adjacent number.
The buying rule
Choose a rating 10–15°F below the coldest overnight low you realistically expect. Reasons: ratings assume a fresh, insulated setup (see the pad section); humidity, wind, fatigue, and dehydration all push your real comfort colder; and an over-warm bag unzips, while an under-warm bag has no fix at 3 a.m.
Standard category guide (REI's convention, widely used):
- Summer: rated +30°F and up
- Three-season: rated +15 to +30°F — the 20°F bag is the default all-rounder for most campers
- Winter: rated +15°F and below
Your pad is half the system
ISO bag ratings are measured on an insulated pad. Lying on cold ground crushes the insulation under you flat — the ground, not the air, steals most of the heat. Pad insulation is rated by R-value (ASTM F3340-18 standard):
| Season | Pad R-value |
|---|---|
| Summer | R 1–2 |
| Three-season | R 3–4.9 |
| Winter / snow | R 5.5+ |
A 20°F bag on an R-1 pad is not a 20°F system. If you sleep cold at temperatures your bag should handle, upgrade the pad first.
Down vs synthetic (one paragraph's worth)
Down insulates more per ounce and packs smaller; it loses insulation when soaked and costs more (hydrophobic treatments narrow the gap). Synthetic is cheaper, insulates somewhat when damp, and is heavier/bulkier for the same rating. Wet climates and budget favor synthetic; weight-conscious dry-climate packing favors down.
Making one bag span more nights
- Colder than rated: wear a dry base layer + hat, use a liner (adds roughly 5–15°F), eat before bed, put a hot-water bottle in the footbox, double up pads
- Warmer than rated: unzip and drape, or sleep on top with the bag as a quilt
Quick worked example
Shoulder-season weekend, forecast low 34°F: expect the campsite to run a few degrees colder than the forecast town. 34 − 10 to 15 → shop a 20°F bag — and if you're a known cold sleeper, check that its COMFORT rating (not lower limit) is near 30°F. Pair with an R-4 pad.
Time ranges by condition
| Condition | Duration | Note |
|---|---|---|
| Summer camping (lows 40°F+) | Bag rated +30°F or warmer | — |
| Three-season (lows 25–40°F) | Bag rated +15 to +30°F — 20°F is the default | — |
| Winter / snow (lows below 25°F) | Bag rated +15°F or lower | — |
| Buffer rule | Rating 10–15°F below expected low | — |
| Pad for 3-season | R-value 3–4.9 | — |
| Pad for winter | R-value 5.5+ | — |
What changes the time
- Which ISO number you read. Comfort vs lower limit differ by ~10°F on the same bag. Unisex/men's marketing usually quotes lower limit; cold sleepers should shop by comfort rating
- Sleeping pad R-value. Ratings are tested on an insulated pad. An uninsulated pad can cost you 10–20°F of real-world warmth — the most common cause of "my bag is under-rated" complaints
- Personal metabolism. Cold sleepers, smaller/leaner bodies, exhaustion, and dehydration all shift comfort colder. The 10–15°F buffer absorbs this
- Moisture + wind. Damp down loses loft; wind strips heat through tent mesh in warm weather. Humid or exposed sites justify the deeper end of the buffer
- Liner + layers. A liner adds roughly 5–15°F and keeps the bag clean; a dry hat + base layer extends any bag. Cheap ways to make one bag span three seasons
Common questions
Why was I cold in a 20-degree bag at 30°F?
Three usual suspects: the 20°F was the lower-limit (survival-leaning) rating and your comfort number was ~30°F; your pad's R-value was too low and the ground drained you; or you went to bed damp, hungry, or dehydrated. Pad first, then rating.
Are women's sleeping bags actually different?
Yes — beyond cut, they're typically labeled by the warmer COMFORT rating and often carry extra insulation in the footbox and torso. The rating convention alone explains much of the "women's bags run warmer" observation.
Is a 0°F bag a safe all-rounder choice?
It's heavier, bulkier, pricier — and sweaty for most 3-season nights. The standard approach: a 20°F bag plus a liner and clothing layers covers spring–fall; rent or buy winter gear separately if you actually winter-camp.
Do sleeping bag ratings degrade over time?
Yes — compressed storage and dirt reduce loft. Store bags uncompressed (hung or in a large mesh sack), wash per the label, and expect a hard-used bag to run warmer-rated than its tag after years of service.
Sources
We cite primary research, expert practice, and authoritative reference. Higher-tier sources weighted heavier. See methodology.
- T1ISO 23537-1 (formerly EN 13537) — Requirements for sleeping bags — The lab standard defining comfort / lower-limit / extreme ratings via heated-manikin testing
- T1ASTM F3340-18 — Standard test method for R-value of camping mattresses — The standardized pad-insulation measurement that made R-values comparable across brands
- T2REI Expert Advice — How to choose a sleeping bag; Sleeping pad R-value explained — The widely-used season categories, buffer rule, and bag+pad system guidance
Gear that helps with this
If you're shopping for the kit this question is about, here are solid places to start on Amazon.
- Three-season sleeping bag (check the ISO comfort rating)See options on Amazon
- Insulated sleeping pad (check the R-value)See options on Amazon
- Sleeping bag liner (adds warmth, keeps the bag clean)See options on Amazon
As an Amazon Associate, AskedWell earns from qualifying purchases at no extra cost to you. These are general category suggestions to help you shop, not a specific endorsement. See our disclosure.
Cite this page
de Vries, P. (2026). What temperature rating do you need for a sleeping bag?. AskedWell. Retrieved 2026-07-16, from https://askedwell.com/pages/what-temperature-for/sleeping-bag-rating
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