Bevel Angles
The Bevel Angle is the inclusive angle of the knife edge. That is to say, a single measurement of the angle between both sides of the edge. Some knife makers will state a bevel angle as being extra sharp at 6 degrees. Although certainly possible, it probably reflects the measurement of only one side of the bevel. A true bevel angle of 6-degrees would be so fine that it would not hold up to much use and require frequent sharpening. Blade thickness is also a consideration, think very thin and very sharp razor blades.
Experience teaches that 17 to 20 degrees is very sharp but needs to be sharpened frequently in professional use. It is also more likely to chip when it hits a bone, and almost certain to chip if it is used to pry joints apart. This edge is quite capable of shaving hair, (a favored but not recommended test of an edge).
A 22-degree to 25-degree bevel angle makes for a usable sharp edge that is stronger and will hold an edge longer than the lesser angles. Still capable of shaving hair, if that’s your thing.
Angles above 25-degrees are not typical for normal use but are often found on survival knives. These bevel angles are very strong and hold up to abusive use. This is also when blade thickness comes into play. If you’re going to attack a rhinoceros you will need a good thick blade, and small bevel angles are just not going to be practical for the knife’s edge.