At what % sodium does a solution become hypertonic? .9% is isotonic, 3% is hypertonic, but where does it change from isotonic to hypertonic? ...2%?

Hypertonic : Hypertonic fluid has a sodium content that is greater than that of serum. Human serum has a sodium content of approximately 154 meq/liter. "normal saline" or 0.9% Normal Saline has the same sodium content as serum. Therefore, anything greater than that serum sodium concentration is a hypertonic solution. Examples of this in commercially available forms are 3% or 7% normal saline.