Sleep System Comfort Estimator
Combines bag rating + pad R-value + estimated overnight temperature to flag a cold one.
Inputs
Result
A natural placement between the calculator and the explanation.
What this solves — and what it doesn't
Most ‘is this bag warm enough?’ questions ignore the pad. A pad R-value of 5 is worth roughly 7 C of effective warmth compared to a basic foam pad. This calculator adds that pad warmth contribution to your bag rating, then adjusts for sleeper type, wind exposure, and whether you’ll eat before bed (which raises core temp for ~90 minutes).
How to read the result
The verdict is ‘Comfortable sleep’ (margin >5 C), ‘OK, may wake cold’ (0 to 5 C), or ‘Cold night — add a layer or liner’ (negative margin).
The biggest hidden lever here is the pad. Many backpackers upgrade their bag when the fix was buying a higher-R pad. The reverse is rarely true.
Limitations
- No humidity adjustment.
- Doesn’t model metabolism disorders or alcohol use.
- Pad warmth contribution is approximate; real pads vary.
Frequently asked questions
Is R-value additive between pads?
Roughly yes for stacked pads: R1 + R2 ≈ R_total. Two R=2 pads under you is about R=4, not 4-like-the-best-one.
Can I use a liner to extend the bag?
Yes — a silk or fleece liner adds 3 to 8 C of effective warmth. Useful in shoulder seasons.
What about sleeping in clothes?
Adds a small amount but compresses loft in the bag. Not a substitute for a proper bag.