A few years back I sewed a bandana for Pocket. It needed to fit her just right and not be too bulky. After several not quite failures, I came up with the perfect pattern. Pocket's bandanas have a slightly scooped neck and are meant to be tied on to fit. Can be worn tighter or looser and should fit necks up to 17.5 inches around (measure your comfortable collar size). Fabric has been washed so little to no shrinking should be expected. Actual length of bandana tying end to end is 24-25 inches.
Wash on cold and tumble or air dry, followed by an iron pressing for best results.
Pocket's perfectly fitting bandana unfortunately contains no right angles and really isn't made for mass production.