What Temperature Sleeping Bag Do I Need in the UK?

Quick answer: for most UK camping from late spring to early autumn, choose a sleeping bag with an ISO comfort rating of about 0°C (around +5°C is enough for lowland campsites in high summer). For year-round use, winter camping, or camping high in the hills in spring and autumn, aim for a comfort rating of −5°C or lower. Met Office 1991–2020 averages put typical UK overnight lows between about −1°C (Braemar in winter) and 13°C (Oxford in July), and it gets roughly 0.5–0.65°C colder for every 100 m you climb.

Last updated: 25 September 2026. Research-based guide: see how we research.

This guide is built from official data rather than guesswork: Met Office climate averages for six representative UK locations, the ISO 23537 sleeping bag standard, the ASTM F3340 sleeping mat standard, and published guidance from UK and international outdoor retailers and brands. Below you will find what the ratings mean, a month-by-month table of typical overnight lows by region, how season ratings map onto real temperatures, and how to pair your bag with the right mat.

Sleeping bag temperature ratings explained

Most reputable sleeping bags sold in the UK carry temperatures tested to ISO 23537-1, the international standard that replaced the older European EN 13537. Both use a heated manikin in a climate chamber, dressed in a single base layer and placed on an insulating mat, to measure how much heat the bag holds in. The result is three numbers:

The gap between the numbers matters. Comfort and limit ratings on the same bag are often several degrees apart, and many brands headline the limit rating because it looks warmer. If a listing gives only one temperature, check which one it is. If it gives no ISO or EN rating at all, treat the figure as a manufacturer claim rather than a tested result.

Remember that the lab test assumes near-still air, dry insulation, a base layer and an insulating mat under the sleeper. Pitch in the wind, sleep on thin foam or crawl in wearing damp clothes and the same bag will feel colder than its label.

What about tog ratings?

Tog is used for duvets and baby sleeping bags. It is not the standard for adult outdoor sleeping bags, so a “tog” figure on a camping bag cannot be compared fairly with an ISO comfort rating. For camping, always look for the ISO 23537 or EN 13537 comfort temperature.

Month-by-month: typical UK overnight lows and the bag you need

The table below uses the Met Office’s published mean daily minimum temperature (1991–2020 averages) for six climate stations that represent popular UK camping areas. That is the average of each night’s lowest temperature over 30 years. Individual nights regularly fall several degrees below average, especially on clear, still nights, so our recommended comfort ratings sit comfortably below the coldest regional average for each month.

Typical overnight low = Met Office mean daily minimum temperature, 1991–2020 averages, for the named climate station. *Princetown figures are approximate: they are Met Office 1981–2010 normals (station at 453 m), as the current Met Office averages page for Princetown resolves to a coastal station and is not representative of the moor. Recommendations are our research-based guidance, not part of any standard.

How to read it: find the month you are going and the area closest to where you will camp. The “campsite / valley” column suits pitches at roughly the height of these stations. If you plan to wild camp on a ridge, a summit plateau or a high tarn, use the “plus height” column. On any trip, a bag that is slightly too warm can be unzipped; a bag that is too cold means a long night.

How much colder is it higher up?

Air temperature falls with height. The Met Office’s regional climate summaries give a decrease in mean temperatures of about 0.5°C per 100 m, and the international standard atmosphere uses 0.65°C per 100 m. In dry air the rate can approach 1°C per 100 m, and the British Mountaineering Council warns temperatures can drop by 1–2°C for every 100 m on the hill. As a working rule:

• Camping 300 m above a valley station: expect roughly 1.5–2°C colder on average.
• Camping 600 m above it: roughly 3–4°C colder.
• Camping 900 m above it: roughly 4.5–6°C colder, before any wind chill.

One exception: on clear, calm nights, cold air can drain into valley floors and hollows, so a sheltered valley pitch can occasionally be colder than a slope above it. Braemar’s cold averages partly reflect its position in a Highland glen.

If you are still choosing a route, the free Peak Outdoor Guide UK trail guides app lists heights for popular walks, which makes it easier to judge how much colder your camp spot will be.

1 to 5 season sleeping bags: what the ratings mean in the UK

Season ratings are a retail convention, not a standard, so one brand’s “3 season” can be warmer or cooler than another’s. Guidance published by UK retailers and brands such as Alpkit, Blacks and The Great Outdoors magazine broadly agrees on these bands:

So, 2 season vs 3 season for the UK? A 2-season bag is fine for lowland campsites from June to August. A 3-season bag with a comfort rating around 0°C is the better single choice for most people, because it covers spring and autumn, upland pitches and the Scottish summer too. Our round-up of the best 3-season sleeping bags for 2026 compares comfort and limit ratings side by side.

If you only buy one bag and camp mainly in England and Wales from spring to autumn, a comfort rating of 0°C is the sweet spot. If you camp in Scotland, sleep cold, or want to camp into November and from March, look closer to −5°C comfort.

Your sleeping mat matters as much as your bag

The insulation underneath you gets crushed flat by your body weight, so most of the heat you lose into the ground goes through your mat. A warm bag on a thin mat will still feel cold. Since 2020 most major mat brands have tested to ASTM F3340, which measures thermal resistance (R-value) in a standard way so you can compare mats across brands. Higher is warmer.

R-values are additive: a closed-cell foam mat under an inflatable mat adds its R-value to the total, and also protects the inflatable from punctures. This is a cheap way to turn a 3-season set-up into a colder-weather one. Because the ISO bag test puts the manikin on an insulating mat, pairing your bag with too thin a mat means you will not get the warmth the label suggests.

Wind chill, damp and the other things ratings don’t cover

The Met Office’s “feels like” temperature accounts for wind and humidity because wind strips away the thin layer of warm air around your body; it notes wind chill can make conditions feel 3 or 4 degrees colder. Inside a well-pitched tent that effect is much reduced, but a draughty pitch, an open door or a bivvy on an exposed ridge will cost you warmth. The UK’s damp air also matters: moisture from breath and condensation can slowly reduce the loft of down insulation over a multi-day trip, while synthetic fill generally keeps more of its warmth when damp.

Personal factors are the biggest variable of all. The ISO comfort rating is based on a standard woman precisely because many people, and women on average, sleep colder than the limit rating assumes. If you know you feel the cold, go one step warmer than the table suggests.

6 practical tips for choosing and using a sleeping bag in the UK

1. Buy on the comfort rating. Compare bags on their ISO 23537 or EN 13537 comfort figure. If you sleep cold, choose a bag whose comfort rating is a few degrees below the lowest temperature you expect.
2. Plan for the coldest night, not the average. The Met Office figures above are averages. Check the Met Office mountain forecast before you go, which gives temperatures at summit level as well as in the valleys, and add the height adjustment for your pitch.
3. Match your mat to your bag. Use an R-value of about 3–4 for 3-season UK use and 4.5 or more for frosty or winter nights. Stack a foam mat under an inflatable one when it gets colder.
4. Pitch out of the wind. Choose a sheltered spot, face the door away from the wind and avoid obvious frost hollows on still, clear nights. More ideas are in our guide on how to stay warm in a tent.
5. Use layers and a liner to extend a bag’s range. Dry base layers, a hat, warm socks and a liner all add warmth, so a 3-season bag can stretch into colder shoulder-season nights. Manufacturers’ warmth claims for liners are not ISO-tested, so treat them as a bonus rather than something to rely on.
6. Keep your insulation dry and lofted. Store the bag uncompressed at home, keep it in a waterproof liner or dry bag inside your rucksack, and air it out whenever you can. Our gear checklist covers the rest of your sleep system, and if this is your first trip, read how to plan your first overnight backpacking trip.

Frequently asked questions

What temperature sleeping bag do I need for the UK in summer?

For lowland campsites in June to August, a bag with an ISO comfort rating of around +5°C is usually enough, because Met Office 1991–2020 averages put July overnight lows at about 13°C in Oxford. For the hills or the Scottish Highlands, choose a comfort rating nearer 0°C: Braemar’s average July low is only about 9°C, and clear nights and altitude push it lower.

Is a 3 season sleeping bag warm enough for the UK?

For spring, summer and autumn, usually yes. Retailer guidance generally puts 3-season bags at a comfort rating from about 0°C down to −5°C, which covers most UK nights from April to October. For winter camping, high camps in early spring or late autumn, or if you sleep cold, you will want a 4-season bag or extra layers and a warmer mat.

Should I go by the comfort or the limit temperature rating?

Use the comfort rating. Under ISO 23537 (which replaced EN 13537), comfort is the temperature at which a standard woman sleeps comfortably in a relaxed position. The limit rating is the temperature at which a standard man, curled up, is just not feeling cold, so it assumes a warm sleeper. The extreme rating is a survival figure only and should never be used for choosing a bag.

What tog sleeping bag do I need for camping in the UK?

Tog is a duvet and baby sleeping bag rating and is not the standard used for adult outdoor sleeping bags. For camping, look for the ISO 23537 (or older EN 13537) comfort temperature instead. As a guide, aim for a comfort rating of around +5°C for lowland summer camping, 0°C for 3-season use and −5°C or lower for UK winter or high camps.

What R-value sleeping mat do I need for UK camping?

Look for an R-value tested to ASTM F3340. REI’s guidance is under 2 for warm weather, 2 to 3.9 for cool weather, 4 to 5.4 for cold weather and 5.5 or more for extreme cold. For most UK 3-season camping, around R 3 to 4 is a sensible target, and R 4.5 or more for frosty or winter nights. R-values add up, so a foam mat under an inflatable adds warmth.

Sources

• Met Office: Oxford location-specific long-term averages (1991–2020)
• Met Office: Buxton long-term averages (1991–2020)
• Met Office: Keswick long-term averages (1991–2020)
• Met Office: Capel Curig long-term averages (1991–2020)
• Met Office: Braemar long-term averages (1991–2020)
• Met Office: historic station data (Oxford; Braemar also used to cross-check)
• Princetown climate table (Met Office 1981–2010 normals)
• Met Office: North East England climate (temperature change with altitude)
• Met Office: Wind chill factor
• Lapse rate (ICAO standard atmosphere)
• British Mountaineering Council: British weather on the hills
• EN 13537 / ISO 23537 temperature ratings
• ISO 23537-1:2022 sleeping bag temperature rating explained
• Mountain Equipment: sleeping bag temperature ratings explained
• REI: how to choose a sleeping pad (R-value bands)
• ASTM F3340 sleeping pad R-value standard FAQ
• Alpkit: how warm should your sleeping bag be?
• The Great Outdoors: how sleeping bag ratings work