To use the change Brush Opacity (instead of the Brush Hardness), based on the vertical drag movement, select Preferences > Tools and uncheck “Vary Round Brush Hardness based on HUD vertical movement”.On Windows: Control + Alt + Right click -drag left/right to decrease/ increase brush size and up/down decrease/ increase brush hardness.On Mac: Control + Option (Mac) –drag left/right in order to decrease/increase brush size and up/down to decrease/ increase brush hardness.Resizing Using the HUD (Heads-Up Display) Scroll down (almost the bottom of the list) and enter any single character to set a new shortcut for Decreasing/Increasing Brush Size. To customize the keys used to increase/decrease brush size and hardness (as many international keyboards do not have brackets), under Edit > Keyboard Shortcuts – choose “Shortcuts For: Tools”.Hold the left/right bracket to continuously decrease/increase brush size.Tap the left/right bracket decrease/increase brush size.

Although I often use the Brush tool as the example, many of these shortcuts also work for other painting tools such as the Pencil, Mixer Brush, Clone/Pattern Stamp, Eraser, Gradient, Paint Bucket and more.

Here are twenty of my favorite shortcuts for the Brush and painting tools in Photoshop.

Square brush in photoshop