Sleeping Bag Temperature Ratings Chart (EN/ISO)

The number printed on a sleeping bag is almost always the limit rating, and a limit rating is a survival figure, not a comfort figure. Under EN 13537 and its successor ISO 23537, limit describes the coldest temperature at which a standard adult male sleeps curled up without waking from cold. The comfort rating typically sits 10 to 15 degrees Fahrenheit warmer. The third number some makers publish, the extreme rating, is a survival-with-injury figure: roughly six hours without death, with a real risk of frostbite and hypothermia. It must never be used to plan a trip.

That is the whole page in one paragraph, and it is the single most misread specification in backpacking. Somebody buys a 20 degree bag, camps on a 20 degree night, shivers until dawn and concludes the bag is defective. The bag did exactly what it was rated to do. The rating was simply never a promise of comfort.

How do the published ratings convert to real night temperatures?

The table below takes the limit ratings manufacturers actually print, adds the comfort band that sits above them, and then adds the practical figure most people want: the night temperature at which you will genuinely sleep well, split by whether you run warm or cold. The warm and cold sleeper columns assume the same bag on the same adequate pad, with dry base layers and a normal dinner.

Use the cold sleeper column if you are not certain which you are. Being 10 degrees too warm costs you a vented footbox and an unzipped side. Being 10 degrees too cold costs you the night, and on a bad night it costs you the trip. The sleep system temperature calculator runs this arithmetic with your pad included, which is the part people leave out.

What does the EN and ISO test actually measure?

It measures a heated manikin, not a person. The test places a thermal manikin, dressed in a standardised base layer set and a hat, inside the bag, on a sleeping pad, inside a climate controlled chamber. Heaters inside the manikin hold its surface at a fixed skin temperature while the chamber is cooled, and the power required to hold that temperature gives the insulation value of the whole system. Those measurements are then run through a physiological model that produces the three published numbers.

• Comfort: the temperature at which a standard adult woman, defined in the protocol as 25 years old, 60 kg and 1.60 m, sleeps relaxed in a normal posture without waking from cold.
• Limit: the temperature at which a standard adult man, defined as 25 years old, 70 kg and 1.73 m, sleeps curled up for eight hours without waking from cold. This is the number printed on the bag in most markets, and it is a survival threshold, not a comfort one.
• Extreme: the temperature at which the standard adult woman can survive roughly six hours without dying of hypothermia, with a strong risk of frostbite and cold injury. It is a survival-with-injury number and it has no legitimate use in trip planning.

Three things about that protocol matter enormously in the field. The chamber has no wind. The manikin does not sweat, does not breathe moisture into the down, and does not go to bed dehydrated after a 24 mile day. And a pad is always underneath, so the published rating already assumes ground insulation that you may or may not actually be carrying. Change any of those and the number stops describing your night.

ISO 23537 replaced EN 13537 and refined the test, but the three-number structure and the standard-man and standard-woman definitions carried over. In practice you can read an EN 13537 figure and an ISO 23537 figure the same way. The important distinction is not which standard was used but whether the bag was independently tested at all.

What pad R value does each rating need?

A temperature rating is a property of the whole sleep system, not of the bag alone, because the test is run with a pad. Sleep on a thinner pad than the test used and the rating overstates your real warmth. This is the most common reason a correctly chosen bag still sleeps cold, and it matters even more with a quilt, since a quilt deliberately deletes the insulation underneath you and leans entirely on the pad.

That last line in the footer is the cheapest fix in the category. R values add, so a Therm-a-Rest Z Lite Sol foam pad at R 2.0 laid under an insulated air pad at R 4.5 gives you a system at R 6.5 for 14 ounces and $60, which is far cheaper than a dedicated winter pad and gives you a backup if the air pad punctures. The inflatable versus foam comparison covers when stacking is worth the bulk, and the sleeping pad roundup lists the published R value for each option.

What are the actual rated bags and quilts worth knowing?

The table below lists the rated sleep insulation covered on this site, with the maker's published temperature rating, the published weight, and how the rating was arrived at. That last column is the one to read carefully, because a big-brand bag with a tested limit rating and a cottage quilt with a maker-assigned comfort rating are not the same kind of number even when the printed figure is identical.

Pair any of those with a pad that actually reaches the R value the rating assumes. The three pads with published R figures on this site are the Therm-a-Rest Z Lite Sol at R 2.0 and 14 oz, the NEMO Tensor Trail at R 2.8 and 15.5 oz, and the Therm-a-Rest NeoAir XLite NXT at R 4.5 and 13 oz. Only the last of those independently supports a 20 degree bag or quilt at its rating, which is why so many sub-10 pound kits are built around it.

Why are cottage quilts rated differently?

Because the test does not fit them, and because it is expensive. EN and ISO testing costs meaningful money per model per length, and the protocol was written around a hooded mummy bag sealed around a manikin. A quilt has no hood, no zip and an open back, and its performance depends on how well it seals to the pad, which is a variable the chamber cannot standardise. Most cottage makers therefore assign ratings from their own fill weight calculations and years of customer feedback rather than paying for a certificate.

The practical consequence is a convention mismatch. Big-brand bags print a limit rating. Cottage quilt makers generally intend their number as a comfort rating, meaning the temperature at which a typical user is comfortable rather than merely alive. So a 20 degree quilt from a respected cottage maker and a 20 degree big-brand bag can be genuinely different products, and the quilt is often the warmer of the two in practice despite weighing less.

Do not treat that as a rule you can lean on. It is a tendency, not a standard. The safe method is to read the maker's own page, find out whether they describe their number as comfort or limit, check the fill weight in ounces rather than the rating alone, and add margin if you sleep cold. Two quilts with the same printed rating and a two ounce difference in down fill are not equally warm. The quilt versus sleeping bag comparison covers the rest of the trade, and the ultralight quilt roundup lists what each maker actually publishes.

Insulation type changes the picture too. Down loses most of its loft when soaked and takes a long time to recover, while synthetic fill retains a usable fraction of its warmth wet and dries faster. A rating tells you nothing about that difference, which is why the down versus synthetic comparison matters as much as the number on the label for anyone hiking in sustained rain.

Why do so many people sleep colder than the rating?

Because the standard sleeper in the test is a construct, and almost nobody matches it on the third night of a hard trip. Every one of the following pushes your real comfort temperature upward, and they stack.

• Being a woman or small framed. The protocol itself acknowledges this by publishing a separate comfort rating derived from the standard woman. Lower average body mass, a higher surface area to mass ratio and different peripheral circulation all mean less heat produced and more heat lost. A 10 degree Fahrenheit margin over the limit rating is a sensible default.
• Being a naturally cold sleeper. Metabolic rate at rest varies widely between individuals. If you use extra blankets at home, you will need extra margin on the trail, and no amount of gear optimisation changes that.
• Being tired. Deep fatigue lowers overnight metabolic heat production and blunts the shivering response. The night after your biggest day is the night you are least equipped to stay warm, which is exactly when people are surprised by it.
• Being dehydrated. Reduced blood volume impairs circulation to the hands and feet. Cold extremities are usually a hydration problem before they are a gear problem.
• Being underfed. Your body burns fuel to make heat overnight. Skipping dinner or under-eating for several days in a row leaves you without the calories to do it. A snack with fat in it before bed is worth more than a liner.
• Being damp. Damp base layers, a bag that has absorbed condensation over four nights, or a shelter dripping onto the footbox all cost real degrees. Down that has taken on moisture over several days can lose a noticeable fraction of its loft with no obvious sign.
• Being under-padded. The single largest and most correctable error. Conduction into cold ground moves heat far faster than convection into cold air, and no bag compensates for a thin pad.

How should you choose a rating for a trip?

Work from the coldest night you could plausibly meet, not the average forecast. Look up the record low for the elevation and season, not just the ten day outlook, then subtract for the fact that valley bottoms, meadows and lake shores collect cold air and routinely run 5 to 10 degrees colder than the ridge above them. Take that number as your target night low and read back up the first table to find the limit rating that covers it.

For most three season backpacking in the mountains of the continental United States, that lands on a 20 degree bag or quilt with a pad at R 4 or better. It is the default for good reason: it covers a frosty night in early season, and it vents adequately on a warm one if the footbox opens or the quilt can be worn loose. A 30 degree bag is a summer and low elevation choice. A 15 or 10 degree bag is the right answer for anyone who genuinely sleeps cold or camps high into the shoulder season, and the weight penalty over a 20 is smaller than people expect.

Then check the whole system rather than the bag alone with the sleep system temperature calculator, and compare specific models on the ultralight sleeping bag roundup. Carry a set of dry sleep clothes you never hike in, eat something before you get in, and accept that the correct margin is the one that lets you sleep, not the one that keeps you technically alive.