The angle you sharpen at decides how a knife cuts and how long the edge lasts. The short answer: 15° for thin, hard Japanese-style knives; 20° for most Western chef's knives.
What the angle actually means
The sharpening angle is measured on each side of the blade. A 15° knife has a narrower, finer edge (about 30° in total). A 20° knife has a sturdier edge (about 40° in total).
When to use 15°
- Japanese-style knives: santoku, gyuto, nakiri, petty knives
- Thin, hard steel blades that came very sharp from the factory
- Precise tasks: slicing tomatoes, herbs, fish, thin vegetables
A 15° edge feels sharper, but it's more delicate. Avoid using it on bones or frozen food.
When to use 20°
- Most Western chef's knives (German-style and most supermarket knife sets)
- Thicker, softer steel blades
- Heavier jobs: pumpkin, root vegetables, cutting around bones
A 20° edge is a bit less keen but holds up longer to everyday use.
Not sure what you have?
Check the manufacturer's website for the factory angle. If you can't find it, use 20°. It's the safe choice for most kitchen knives, and you can always go finer later.
The hard part is holding the angle
Whichever angle you choose, the edge only gets sharp if you hold it consistently. That's hard to do by hand on a whetstone. A rolling sharpener with a magnetic angle block, like the Sharpsmith rolling knife sharpener, holds the knife at exactly 15° or 20° for you.