It kind of depends. Hollofil is an older insulation and it requires quite a bit of the stuff to keep you war as compared to down or some of the newer synthetics. Also if your bag is old, the rating will be greatly diminished. If you want something to go by, look at the actual loft. You should see something like 6" of loft for a 0* bag. And remember if it says 0*, that the extreme end of comfort. A 0* bag is Comfortable down to about 15 before you start to feel chilled. A 20* bag may be 30 and so on.
Riot