While creating new brushes in PaintTool SAI requires comfort with software coding, changing the sizes of native brush sizes isn't as complicated. The toughest aspect of resizing brushing in this application is not being able to right-click and establish a new brush size. Despite this limitation, Paint Tool SAI is a sufficient free image-editing application that enables creating digital art by making use of quick keys to create various sized brush strokes. Using this method to change the size of this application's airbrush and standard brush can add complexity and detail to your work.
Click the "Brush" or "Airbrush" tool.
Increase the size the selected brush by pressing the "]" key.
Decrease the size of the brush in use by pressing the "[" key.
Select an airbrush or standard brush size from within the "Advanced Settings" area if you do not want to use quick keys to resize brushes.
You may need to increase the size of Paint Tool SAI's application window to view its "Advanced Settings" area.