…which makes it an EN rating of 20. It's important to know how the EN rating scale works, since it uses both men and women in it, as well as comfort and lower limit. Wiki puts it this way:
Upper Limit — the temperature at which a standard man can sleep without excessive perspiration. It is established with the hood and zippers open and with the arms outside of the bag.
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 minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia (though frostbite is still possible).
Note the genders, as well as sleeping positions required to achieve the ratings. Realize that most bags are sold with the lower limit rating as their classification title, like the Kelty 20, being only "comfortable" down to 31 degrees for a woman.