What do comfort and lower limit ratings mean?

Under the EN 13537 / ISO 23537 standard, the comfort rating is the temperature at which an average woman can sleep comfortably. The lower limit is the temperature at which an average man can sleep for 8 hours. The extreme rating is the survival-only temperature. Always choose a bag rated to the comfort temperature for your expected conditions.

Why does altitude affect sleeping bag choice?

Temperature drops approximately 1°C for every 150 metres of altitude gain (the lapse rate). A campsite at 900m will be roughly 6°C colder than sea level. Additionally, exposed high-altitude campsites often experience stronger winds, further reducing the effective temperature.

Do I need a different bag for cold sleepers?

Yes. Cold sleepers should choose a bag rated 3-5°C below their expected minimum temperature. Factors that make you sleep cold include: being female, low body mass, fatigue, dehydration, and age. A sleeping bag liner can add 2-5°C of warmth.

How important is the sleeping pad?

Very important. Most heat is lost through conduction to the cold ground, not through the top of the sleeping bag. A sleeping pad with an appropriate R-value is essential. Without a pad, even a -20°C sleeping bag will feel cold on frozen ground.

CampCalcs

Sleeping Bag Temperature Calculator

Find the right sleeping bag rating based on expected conditions, altitude and personal factors.

Expected Low Temperature

Forecast minimum overnight temperature

Campsite Altitude

Sleep Type

Do you tend to feel warm or cold at night?

Using a sleeping pad

Sleeping pad provides critical ground insulation

Sleeping in shelter (tent/tarp)

Shelter reduces wind chill effect

How We Calculate This

This calculator adjusts the expected temperature for various factors to recommend a sleeping bag comfort rating.

Effective temperature

Effective temp = Expected temp + Altitude adjustment + Sleep type adjustment + Pad adjustment + Shelter adjustment

Adjustments applied

Altitude: -1°C per 150m of elevation
Warm sleeper: +2°C
Cold sleeper: -3°C
No sleeping pad: -3°C
No shelter (open bivvy): -2°C

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.