Which comfort rating should your sleeping bag have?

The figure to read on a sleeping bag’s label is the comfort rating, and it should sit close to the coldest night you expect — a little below it for a margin, well below it if you sleep cold. The limit and extreme ratings are not for choosing.

The bag is only half the night, though. The ground draws heat through your back, and only the mat stops it: its R-value decides whether a good bag gives a good night. The tool below answers both questions at once, and tells you which of the two is the weak link.

The benchmarks come from the site’s guides: how to choose a sleeping bag for the ratings on the label, sleeping well in spring and autumn for R-values, and winter camping below freezing.