A family of closed-form formulas for calculating minimum corner-fill radii in planar sections of tube hydroformed products is introduced. Corner forming limit diagrams relating the limiting major strain to the minimum corner-fill radius are introduced. The theory accounts for friction effects and accommodates regular shaped polygon die sections. This effort represents an exploration into a method for design and analysis of tube hydroforming processes without employing the finite element method and while using a closed form approach for capturing friction effects. Good agreement with experimental results is observed.