Ray Jardine Formula Calculator
Ray Jardine developed this crude, but useful formula to determine how warm a sleeping bag is. The method measures the thickness of the sleeping bag which will be covering your body. Do not measure the bottom of the sleeping bag, as this does not provide warmth, only the section above you. Find this measurement, in inches. Once you have this, plug it into this Jardine formula or use the calculator below.
The formula is:
Warmth = 100 - (40 x T)
Where T is the thickness, in inches, of your sleeping bag.
Enter your sleeping bag's thickness:
Sleeping Bag Warmth: F
This formula is a rouch estimate. It becomes less exact for extremely thick or thin sleeping bags.