Sleeping Gear
Sleeping bag temperature ratings explained: ISO 23537 comfort vs limit, down vs synthetic, pad R-values, bivvy bags, quilts and hammock insulation.
Calculator · Gear
Sleeping Bag & Pad Calculator
Which comfort rating and pad R-value you need for the night’s low, your shelter and sleep type.
Will your sleeping bag and pad be warm enough? Enter the expected night low, your shelter, the wind and how you sleep – the calculator shows the comfort rating your bag should have and the minimum R-value for your sleeping pad.
Bag comfort rating
≤ 3 °C
EN/ISO 23537
Limit rating
≤ -2 °C
Pad R-value
≥ 4
Bag type
3-season bag
Pad options
| Pad | R-Value | Enough? |
|---|---|---|
| Foam pad | R 2.0 | — |
| Self-inflating pad | R 3.5 | — |
| Insulated air pad | R 4.5 | ✓ |
| Foam + insulated air pad | R 6.5 | ✓ |
| Winter air pad + foam | R 8.5 | ✓ |
How is this calculated?
Needed comfort rating = night low + shelter (+3 tent, +1 tarp/bivvy) + sleep type (+3 warm, −5 cold) + wind (−2 breezy, −4 exposed) + warm layer (+3) + liner (+2). Limit ≈ comfort − 5 °C. Pad R-value by ground temperature: >10 °C R2, >5 °C R3, >0 °C R4, >−10 °C R5, >−20 °C R6, colder R7+.
How to use the sleeping bag calculator
- Enter the expected night low – check the forecast for the coldest hour, usually just before dawn.
- Choose whether you sleep warm, average or cold.
- Select your shelter (tent, tarp, bivvy or open, hammock) and the wind at camp.
- Tick if you sleep in a warm layer (fleece or puffy) and if you use a liner.
How it is calculated
The required comfort rating starts from the night low and is adjusted: a tent adds 3 °C, a tarp or bivvy 1 °C, a hammock nothing. Warm sleepers get +3 °C, cold sleepers −5 °C. Wind takes 2 °C (breezy) or 4 °C (exposed) away. A warm layer adds 3 °C and a liner 2 °C. The result is the comfort rating (EN/ISO 23537) your bag should have or beat; the limit rating is about 5 °C lower.
Example: night low 2 °C, average sleeper, tarp, sheltered, sleeping in a fleece – you need a bag with a comfort rating of 6 °C or lower.
The pad R-value (ASTM F3340) follows the night low as a proxy for ground temperature:
| Night low | Minimum R-value |
|---|---|
| above 10 °C | R 2 |
| 5 to 10 °C | R 3 |
| 0 to 5 °C | R 4 |
| −10 to 0 °C | R 5 |
| −20 to −10 °C | R 6 |
| below −20 °C | R 7+ |
Practical tips
- Buy by the comfort rating, not the limit – the limit describes a curled-up, cold night.
- R-values add up: a foam pad (about R 2) under an insulated air pad is a cheap way to sleep warmer in winter.
- In a hammock use an underquilt – insulation compressed under your body does not keep you warm.
- Eat something fatty and pee before sleeping, and wear a dry hat and socks.
- These are estimates. People differ a lot, so test your setup close to home first.
FAQ
What does the comfort temperature of a sleeping bag mean?
Under EN/ISO 23537 the comfort rating is the temperature at which a standard adult sleeps comfortably in a relaxed position. The limit rating is the temperature at which you can sleep curled up for about eight hours without shivering – it is not a comfortable night.
What R-value do I need for my sleeping pad?
Roughly R 2 for summer nights above 10 °C, R 4 around freezing and R 5–6 for winter. R-values of stacked pads add up.
Why am I cold in my sleeping bag even though it is rated warm enough?
Usually the ground steals heat because the pad is too thin, or you sleep cold, are tired, hungry or damp. Wind through an open shelter also cools you. Improve the pad first, then add a warm layer or liner.
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