Select an object. > Modify panel > Modifier List > Object–Space Modifiers > Spherify
Select an object. > Modifiers menu > Parametric Deformers > Spherify
The Spherify modifier distorts an object into a spherical shape. This modifier has only one parameter: a Percent spinner that deforms the object, as much as possible, into a spherical shape.
The success of the operation depends on the topology of the geometry to which it's applied. For example, a cylinder with no height segments will result in little change. Adding height segments will result in a barrel at 100 percent. Adding cap segments will produce a sphere.
To use Spherify to distort a box:
Create a box in the viewports. Set Length Segs, Width Segs, and Height Segs to 10.
As you lower the Percent setting, the object gradually regains its original boxy shape.