jats:titleABSTRACT</jats:title> jats:pWe investigate the reliability of mass estimators based on the observable velocity dispersion and half-light radius jats:italicR</jats:italic> jats:subh</jats:sub> for dispersion-supported galaxies. We show how to extend them to flattened systems and provide simple formulae for the mass within an ellipsoid under the assumption the dark-matter density and the stellar density are stratified on the same self-similar ellipsoids. We demonstrate explicitly that the spherical mass estimators give accurate values for the mass within the half-light ellipsoid, provided jats:italicR</jats:italic> jats:subh</jats:sub> is replaced by its “circularized” analog jats:inline-formula jats:tex-math

</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlaa40e0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. We provide a mathematical justification for this surprisingly simple and effective workaround. It means, for example, that the mass-to-light ratios are valid not just when the light and dark matter are spherically distributed, but also when they are flattened on ellipsoids of the same constant shape.</jats:p>