Bag + Pad Temperature / R-Value Matcher

The question behind every sleep-system purchase: what bag rating and pad R-value do I actually need? Enter your destination's overnight low and your sleeper type and this matcher returns the bag ISO 23537 Comfort rating AND the minimum pad R-value you need — as a paired system, because a warm bag on a cold pad still sleeps cold. It's the lesson that started this site: I once paired a bag "rated to 20°F" with a cheap summer pad and froze all night, because the cold ground pulled the heat straight out from under me. Get both halves right and you sleep warm.

The coldest temperature you expect overnight. Check the forecast low, then subtract a few degrees of margin if it's exposed or high-altitude.

How warm do you sleep?

Cold sleepers (often women, smaller frames, or anyone who runs cold) should build in extra margin — buy to the Comfort rating, never the Limit.

Season nudges the pad R-value: snow and frozen ground pull far more heat than cool autumn dirt, so winter needs a much warmer pad even at the same air temperature.

How this is calculated

The matcher uses the published lab standards, not personal testing: bag warmth is the ISO 23537 Comfort/Limit rating and pad warmth is the ASTM F3340 R-value, with the R-value-by-season thresholds drawn from the standard's published guidance. It targets a bag whose Comfort rating sits at or below your overnight low (with margin added for cold sleepers and colder seasons), and a pad whose R-value matches the ground heat-loss for that season. These are lab figures — real-world warmth varies with the sleeper, the pad, the shelter and the conditions, and no rating is a survival guarantee. Buy to the Comfort rating and build in margin for cold trips.

New to this? Start with the sleep-system guide → Got your rating? See the best backpacking sleeping bags → Got your R-value? See the best backpacking sleeping pads →