How to use the Brush Size & Shape Guide
- Choose your medium. Pick Watercolor, Acrylic, Oil or Gouache at the top. Every shape’s list of best uses and its sample mark switch to that medium.
- Ask “which brush for…”. Press Washes, Lines, Blending, Texture or Details. The shapes that suit the job are numbered in order of preference, the rest fade back, and the first choice opens automatically. Press the same chip again to clear it.
- Open any shape. Click one of the twelve cards to see the brush, a typical mark it makes, what it does best in your medium and, when a job is selected, how it ranks for that job.
- Check fibers and sizes. Hair and fiber compares sable, synthetic, hog bristle and squirrel. What size numbers mean shows rough widths for numbered rounds and exact widths for flats sold by the inch.
- Take it with you. Copy starter set puts a five-brush shopping list for your medium on the clipboard; Download cheat sheet (PNG) saves a printable page of all twelve shapes.
Shape matters more than size
The mark a brush leaves comes mostly from the shape of its head. A round makes a line that swells as you press and thins as you lift. A flat makes a stroke as wide as the brush, with a crisp edge on each side, and turns into a thin line when you pull it sideways. A filbert sits between the two: flat enough for broad strokes, rounded enough that the ends of each stroke stay soft. Learn what those three do and you can already paint almost anything; the other shapes are specialists that do one job faster.
Fiber decides how the head behaves when it is loaded. Natural hair has a scaly surface that holds water, so a kolinsky sable round (kolinsky is in fact a weasel, not a sable) carries enough for a long wash and still springs back to a point. Squirrel holds even more water but barely springs back, which is perfect for a mop and frustrating for detail. Hog bristle is stiff and splits at the tip into “flags” that grip heavy oil paint and leave the brushwork visible. Modern synthetics imitate all of these at a fraction of the price and survive acrylic, which dries fast and is hard on natural hair.
Medium shifts the balance. Watercolor rewards brushes that hold and release a lot of water evenly; oil and heavy acrylic reward stiffness, because the brush has to push paint around instead of letting it flow. That is why the same filbert is a soft blending tool in oil and a petal-maker in watercolor.
How brush sizes are numbered
There is no shared standard. A size 8 round from one maker can be as wide as another’s 10, and some brands number their oil and watercolor lines differently. Two rules help:
- Rounds are sold by number. Smaller numbers are thinner. Below 1 the sizes count down with zeros: 0, 00 (2/0), 000 (3/0), down to tiny spotters. As a rough guide, a #2 is about 2 mm across at its widest, a #6 about 4 mm and a #12 about 7 mm, but expect a size or more of variation between brands.
- Flats and wash brushes are often sold by width. A 1/2 in flat is close to 12.7 mm wide, a 3/4 in flat 19.1 mm and a 1 in flat 25.4 mm. Those labels are far more reliable than numbered flats, whose width again depends on the maker.
| Job | Small painting (up to about 9 × 12 in) | Larger painting (16 × 20 in and up) |
|---|---|---|
| Main shapes | Round #8–10 or 1/2 in flat | 1 in flat or larger round |
| Details | Round #2–4 | Round #4–6 |
| Lines | Rigger #1–2 | Rigger #2–4 |
| Washes and backgrounds | 3/4 in flat or small mop | 1–2 in wash brush or large mop |
When you shop in person, compare the actual hair, not the number on the handle. If you plan the painting first, the Paper Size Chart and Standard Canvas Sizes Chart help you match brush widths to the surface.
Tips from practice
Buy one good round before five cheap ones. A round that holds a point does the work of several brushes. A cheap one that splays forces you to buy a detail brush, a liner and a spotter to cover for it.
Keep watercolor brushes away from acrylic. Acrylic dries in the belly of the brush, right next to the ferrule, and stiffens it for good. Give acrylic its own synthetic set and rinse it often.
Never leave a brush standing on its head in the water jar. The hairs bend permanently within minutes. Rinse, reshape the tip with your fingers and dry brushes flat or hanging head-down.
Use the edge of a flat before reaching for a liner. Pulled sideways, a 1/2 in flat makes a crisp line exactly as long as you want, which is often faster than switching brushes. For mixing the colors those strokes carry, try the Watercolor Mixing Chart Builder.