Updated: Jan 30, 2020
No two knives are the same - neither in terms of angles, nor the steel they have been made from.
The correct or best angle is determined by the knife's design, use, steel and type.
As a rule of thumb, the lower the angle, the less durable the edge becomes. Think of a razor, for example. Its low angle makes it extremely sharp, but you won’t be able to cut through tougher material without damaging the blade.
The two main types of knives are European (mostly German) and Asian (mostly Japanese). While Japanese knives traditionally have a single bevel, i.e. they are sharpened on one side of the blade only, the vast majority of Japanese knives manufactured for and sold in the U.S. have double bevel blades. German knives always have double bevel blades.
When we are talking about an angle, we are always talking about the angle on one side. Putting a 20-degree angle on a double bevel blade means putting 20-degrees on each side, i.e. the edge of your knife will have an angle of 40 degrees in total.
A 17 to 20-degree is the best knife sharpening angle for to the majority of all kitchen knives, with most western knives falling into the 20-22 degree category. Asian knives sold in the U.S. usually have a slightly lower angle and both sides are sharpened to about 15 degrees.
European knives are generally made from a softer variety of steel that makes them a little more forgiving to the high-impact style of chopping traditionally used in Western cooking. Putting a low degree angle on the blade would make them very sharp but also more prone to damage, i.e. they would require more frequent sharpening. Asian knives are made from a tougher, yet more brittle steel, which means they can take a lower degree angle, given that they are used in the intended way.
Knives that need to withstand tougher materials, such as hunting and pocket knives, will be sharpened to a degree between 22 and 30 degrees as that works best on them.