Or any other dimension, as the Fit button will fit the texture to it. Take some care using this Fit button though, as you may get overstretched textures. That often looks bad, and with extraordinary scale values, you could get some errors too.
Oh, and when you're moving that brush, there's a button in the upper button row that toggles Texture Lock (it's a button with a big T on it). Handy for moving brushes without the texture shifting. You'll see.