[header] How to choose a sleeping bag for backpacking [title] Select a backpacking sleeping bag rated for temperatures you anticipate during your trip. [step] Prior to 2009, each sleeping bag manufacturer had its own temperature rating system. However, in 2009, many manufacturers adopted the european norm (en) 13537 testing methodology, so now temperature ratings are more consistent across sleeping bag brands. 
There are 4 general categories of en sleeping bag temperature ratings. The ratings are calculated based on users wearing 1 layer of clothing and a hat, and utilizing an insulated pad under the sleeping bag.