Below is a table with the New European Union ratings for sleeping bag warmths. Most quality sleeping bag manufacturers use this system which helps the customer to make a clearer choice when trying to decide what bag to go for. However this should only be used as a rough guide as there are many variables to consider, for example, how well fed and hydrated you are. How wet and cold you are when you get in the bag. How good your sleepmat is and so on.
EU Rating
Description
Comfort
The temperature at which a standard woman can expect to sleep comfortably in a relaxed position
Lower Limit
The temperature at which a standard man can sleep for eight hours in a curled position without waking
Extreme
The mimimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia(though frostbite is still possible)
