At what temperature does a quilt stop being enough?
The margin nobody states between the forecast and your sleeping bag
Ask any guide what temperature rating you need and the answer is the forecast. That is not what the planner asks for, and the difference is a single constant that almost nothing published states out loud.
5 °Cadded to every night low, before a rating is asked for
It plans to 5 °C below the night low you describe. Not because the forecast is wrong, but because the number a rider gives is a typical night rather than the coldest one, a comfort rating and a limit rating are different claims about the same bag, and a bag that is exactly adequate has nothing left when any of that goes against you.
The four answers, and what each one asks for
| Your answer | Night low | Bag rated to |
|---|---|---|
| Below freezing | -5 °C | -10 °C |
| Near freezing | 2 °C | -3 °C |
| Cold but not freezing | 8 °C | 3 °C |
| Mild | 15 °C | 10 °C |
Two things follow. A rider who reads the forecast and buys to it has bought one margin short of what the plan asks. And the figure moves in steps rather than smoothly, because the interview offers four answers rather than a slider — so the honest question is which of the four your ride is, not what tonight will be.
What this cannot tell you
Which bag. Nothing in the planner holds a weight, a price or a maker, because none of those were measured. It holds a figure to hit, and the figure is above. Whether a given bag actually meets its own rating is a question about that bag, and this page has not tested one.
Every claim above, and how it is known
- DERIVEDThe planner adds a fixed margin of 5 °C between the night low you give it and the rating it asks for.
- DERIVEDAt “Below freezing” (-5 °C) the requirement is a bag rated to -10 °C.
- DERIVEDAt “Near freezing” (2 °C) the requirement is a bag rated to -3 °C.
- DERIVEDAt “Cold but not freezing” (8 °C) the requirement is a bag rated to 3 °C.
- DERIVEDAt “Mild” (15 °C) the requirement is a bag rated to 10 °C.
Other notes worked the same way
- I have bags for a weekend. Do I need more for two weeks?
Two weeks asks for the same list a weekend does
- My bike is a size M. Will this bag fit?
A frame size is a name; these are the measurements that decide
- Tent or tarp, down or synthetic — does the planner pick, or do I?
Where the planner picks for you, and where it will not
Every figure here came out of the same rules that answer the interview, so it moves when they do. Yours differ wherever your answers differ.