We construct a volume preserving map U p from the p-ball B p (r) = x ∈ R 3 , x p ≤ r to the regular octahedron B 1 (r ), for arbitrary p > 0. Then we calculate the inverse U −1 p and we also deduce explicit expressions for U ∞ and U −1 ∞ . This allows us to construct volume preserving maps between arbitrary balls B p (r) and B p (r), and also to map uniform and refinable grids between them. Finally we list some possible applications of our maps.