Heel height is what the dancer can comfortable control and balance. Nothing worse than a pretty faced dancer who wobbles and bobbles on the floor. If you can make quick, balanced, body changes on a 4" heel so be it, but if you bobble on a 3" heel - stay at a 2.5" or lower heel. In the U.S. there is no hard rule how high a shoe heel must be.

Not all shoe brands fit the same, just like different clothing manufactures you might wear a different size in. Try the shoes on, if you have gaps and your feet slide - move to a smaller shoe.