The first thing you need to do is provide your personal definition of "stability".

From a pure physics standpoint, an object is stable (i.e., won't topple over) if the vertical from its center-of-mass passes through the base when tilted to a given angle. Stability is then quantized to be the angle at which this isn't true and the object will tip over.

As an example, an object with its COM one foot above the center of its three foot diameter circular base can be tilted to an angle of 90 - atan(1/1.5) = 56.3 deg above horizontal before tipping.