Are you yourself spinning the fiber? If so, here's one method, but you need to have a sensitive scale (kitchen scale, grams) to make it work.
Pull off a small amount of fiber (maybe 10 grams) and spin it. Double it back on itself for a two-ply yarn and wind it on a niddy-noddy of known length.
You now know how many yards of two-ply yarn you can spin from 10 grams of fiber.
There are approx. 450 grams in 1 lb, but weigh the fiber on the gram kitchen scale to check what you have. Multiply the number of yards you spun (span?) out of 10 g as a proportion to learn the number of yards you could expect to spin out of 450 g. (Hmm. Looks to me like 45 times as many yards!)
Do the patterns for the scarf and hat list yardage?
And: is the gauge shown for the scarf and hat similar to that you can get with the two-ply yarn?
If not, adjustments will need to be made, either towards a three-ply yarn (and a Lazy Kate for spinning three plies down into one yarn) or maybe different patterns for scarf/hat. Or...the usual sort of thing with needle sizes.