There are many, many Paintbrush sizes out there and you have to just experiment with different sizes, until you find your perfect size for you. It will also depend on what you want to do with it. For painting details such as fasces, I like to use a round sable brush in 4, 6, and 8. But if I want to just paint the background, I prefer to use a bigger size flat, sturdy brushes like size 10 or 12.
The last thing that you need to know is that there are different types of brushes, which get divided into 3 categories.
- Round brush: Exactly what it sounds like. Rounded with a pointed tip. Works well for painting details, but when bought in a big size also good for big surfaces and flat washes.
- Mop brush: This is similar to a round brush, but just a bit more flimsy. This is used for laying large areas of colours quickly.
- Flat brush: You guest it, this brush is flat. It is good for painting large areas.
That's what I would call the basics. Now this is the same with almost every art supply and technique.T he best way to learn is to just experiment. A last tip: do not buy cheap brushes, or else the hairs will start to fall out and stick to whatever you are painting.