Warmth-to-Weight Comparator

Warmth-to-weight is the backpacker's core metric — the most warmth for the least carried grams. Enter a bag's temperature rating and its packed weight (add fill power if you have it) and this comparator scores it, so you can line up two or three candidates and see which one earns its place in your pack. It's how I decide what to carry: the warmest bag isn't worth it if it's a brick, and the lightest bag isn't worth it if you shiver all night. The score finds the balance.

Enter at least one bag. Add a second or third to compare them head-to-head. Weight can be ounces or grams — pick the unit once and keep it consistent.

Weight unit

How this is calculated

The score is derived from published specs only — the bag's ISO 23537 temperature rating against the manufacturer's published packed weight. It rewards a colder rating (more warmth) and penalises weight, so a 20°F bag at 1.8 lb scores higher than a 20°F bag at 3 lb. Fill power, if you enter it, gives a small nod to higher-quality down (more loft per gram). It's a relative framing for comparing candidates, not an absolute warmth measurement. These are lab figures, not personal testing; real-world warmth varies with the sleeper, the pad, the shelter and the conditions, and no rating is a survival guarantee. Pair any bag with a pad whose R-value matches your season — a warm bag on a cold pad still sleeps cold.

New to this? Start with the sleep-system guide → Find your numbers first: the sleep-system matcher → Compare bags: best backpacking sleeping bags →