The temperature ratings provided by sleeping bag manufacturers can be imperfect, and it would be unwise to expect a 30-degree bag to keep you warm when temperatures dip below freezing. If you only plan to use your bag during the summer, a 30-degree bag is a good bet, while a 20-degree bag is appropriate for most shoulder-season activities. If you plan to do winter camping, or live in a more extreme temperate zone, consider a 10- or 0-degree bag (or check out our cold-weather pick). Keep your own preferences in mind—a bag that is warm enough for another person might be too cold for you—and be sure to pick a sleeping pad with an appropriate R rating.