While most manufacturers provide sleeping bag ratings to describe the warmth of their bags, these temperature guidelines are sometimes confusing - and they can vary from one company to another.
To add to the confusion, what is comfortable for one person at a certain temperature might be much too cold or warm for another person in the very same conditions.
Let me demystify sleeping bag temperature ratings for you.
Some sleeping bag ratings are season-based.
A summer bag can be used at temperatures of about 35 degrees Fahrenheit and above. (That's above 2 degrees Celsius.)
If you will be camping only in the heat of the summer, in locations that don't get too cool at night, this type of bag will work for you.
A three season bag is suitable for temperatures between about +10 and +35 F.
That's -12 to +2 Celsius.
A three season bag is appropriate for many camping families. It will keep you warm on cool summer nights.
A cold weather bag can be used for temperatures of between about -10 and +10F.
That's -23C to -12 Celsius.
If you are going to camp in the spring or fall, or at higher altitudes, you'll appreciate the warmth of a cold weather bag.
An extreme cold weather bag is suitable for temperatures below -10F. (That's -23C.)
Most families won't need this type of sleeping bag.
Other sleeping bag ratings specify the temperature at which the manufacturer thinks the bag should be used.
As a general rule, choose a bag that is rated for lower temperatures than you expect to encounter.
The company may specify a temperature range, or they may give just one number.
If a range is specified (eg 20F to 70F/-6C to +21C), that means that the bag will keep you warm within that temperature range.
It doesn't mean that you can't use the bag if the temperature is above the range. You can always unzip the bag, or lie on top of it.
If just one number is specified (eg -14F/-10C), that is the lowest temperature at which they recommend using the bag.
The temperature rating is just one piece of information. There is more to know.
Sleeping bag ratings vary from brand to brand. What one company calls a 0 degree bag might be rated a 10 degree bag by another company.
Respected outdoor equipment companies like Mountain Equipment Coop and REI do rigorous testing of their sleeping bags. I trust their ratings.
In general, I would be less likely to trust the temperature ratings of cheap or "discount" brands.
People vary widely in their preferred sleeping temperature. (If you've ever shared a bed with someone who kicked off the covers while you struggled to pull the covers back up, you'll know what I mean!)
If you are someone who "sleeps cold", you may want to choose a bag that is rated for even colder temperatures than you expect to encounter.
Choosing the proper sleeping bag is just part of staying warm while camping. Here are some other factors to consider.
The best sleeping bag in the world won't keep you warm if you are lying on the cold ground. A sleeping pad will raise you off the ground and help to keep you warm.
A liner can make your bag more versatile. Click here to learn how.
There are lots of things you can do to boost your warmth and comfort. Learn how to stay warm in a sleeping bag here.