As others have said - it depends on your quilt. I've made 2 quilts with piano key borders. One was uniform, and carefully patterned (5 colours, repeating around the quilt). I picked the strip size as someone else said - to fit the quilt size evenly (and in my case, to round out the colour pattern nicely). My other quilt was done from strings - so my piano keys are all different sizes, from leftover string sets. Worked well for that quilt.