Sleeping Bag Comfort Rating Calculator

The EN 13537 (now ISO 23537) is the European standard for testing and rating sleeping bag temperature performance. It uses a heated manikin to measure heat loss and assigns three key temperature ratings: Comfort (for women), Lower Limit (for men), and Extreme (survival). This standard ensures consistent, comparable ratings across brands.

Comfort is the temperature at which an average woman can sleep comfortably in a relaxed position. Lower Limit is for an average man in a curled-up position. Extreme is the minimum survival temperature for 6 hours (risk of hypothermia below this). Typically: Comfort ≈ Lower Limit + 5°C, and Extreme ≈ Lower Limit − 10°C.

On average, women have a lower resting metabolic rate and less muscle mass than men of the same weight, which means they generate less body heat during sleep. Additionally, women typically have a higher surface-area-to-volume ratio, causing faster heat loss. The EN/ISO standard accounts for this by providing a separate Comfort rating for women, which is typically 4–5°C warmer than the Lower Limit for men.

The R-value measures a sleeping pad's thermal resistance. Under your body, the sleeping bag's insulation is compressed and loses most of its loft, so the pad provides the primary insulation from the cold ground. A pad with R-value 3–4 is adequate for 3-season use. For winter camping, an R-value of 5+ is recommended. Using no pad or a very thin pad can reduce your bag's effective warmth by 5°C or more. The EN/ISO test assumes a pad with R-value ~4.8.

No. The EN/ISO ratings provide a standardized comparison but cannot account for all individual variables. Your personal comfort depends on metabolism, body fat, hydration, fatigue, clothing, wind, humidity, and even what you ate before sleeping. Always treat the ratings as a guideline and add a 5–10°C safety margin for critical trips. Use this calculator's personalization panel to fine-tune the rating for your specific situation.

1. Check the lowest expected temperature for your destination and season. 2. Choose a bag whose Comfort rating (for women) or Lower Limit (for men) is at least 5°C below that expected low — this gives you a safety margin. 3. Use this calculator to personalize the rating based on your individual factors. 4. Don't forget to pair it with an adequate sleeping pad!