Sleeping Bag Temperature Rating Chart
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A sleeping bag's printed temperature rating is not the temperature at which an average person sleeps comfortably; it is usually the survival limit, and buying to that number is the single most common reason campers end up shivering at 2am. This chart explains the standardized EN/ISO rating system's three numbers and gives realistic temperature ranges for the seasons most car campers actually sleep in.
The three numbers on a standardized rating
Comfort rating: the temperature at which a standardized cold-sensitive sleeper (modeled as a woman) can sleep comfortably in a relaxed position all night. This is the number to actually plan around for a good night's sleep, not the headline number most bags are marketed by.
Limit rating: the temperature at which a standardized warm sleeper (modeled as a man) can sleep in a curled, defensive position without waking from cold, meaning some discomfort is expected. This is usually the number printed largest on the bag and in marketing, and it typically runs 5-10°C (9-18°F) colder than the comfort rating for the same bag.
Extreme rating: the lowest temperature at which survival without hypothermia is possible for six hours, with significant risk of frostbite and discomfort. This number exists for safety planning in an emergency, not as a target for a planned night's sleep, and should never be treated as a usable comfort figure.
Realistic bag ratings by camping season
Summer car camping (comfort down to about 10-15°C / 50-59°F): a lightweight bag rated around this comfort range covers most warm-weather trips without overheating, and many summer bags can be fully unzipped and used as a blanket on hot nights.
Three-season camping (comfort down to about 0-5°C / 32-41°F): the most versatile single bag for a car camper who goes out spring through fall, covering cool nights without the bulk of a true winter bag.
Cold-weather or shoulder-season camping (comfort down to about -10 to -5°C / 14-23°F): needed for late fall, early spring, or higher-elevation trips where nighttime temperatures drop well below freezing.
Winter camping (comfort down to -20°C / -4°F or colder): a specialized, bulkier, and more expensive category, generally overkill for anyone not specifically planning winter trips, and uncomfortably warm if used in milder conditions.
Buy several degrees colder than your coldest expected night
Choose a bag rated at least a few degrees colder in comfort rating than the lowest temperature you actually expect to camp in, since it is far easier to vent an overly warm bag by unzipping than to add meaningful warmth to an underrated one mid-trip. Personal cold tolerance, whether you sleep on an insulated pad, tent ventilation, and even what you eat before bed all shift how a given rating actually feels, so treat the comfort number as a starting estimate rather than an exact guarantee.
The rating on the bag assumes an appropriately insulated sleeping pad underneath it, since a sleeping bag's insulation is compressed and largely ineffective against the ground where your body weight rests, so a high-quality bag paired with a low R-value pad will still sleep cold regardless of what the bag's tag promises.