"Estimated diameter" refers to an approximate measurement or size of something. It is a guess or estimation of the width or distance across an object or space. Full definition
Potential super-Earths — all with estimated diameters (or radii) between 1.5 and 2.2 that of Earth's but with close - orbiting periods of less than 41 days — that were found and released by the Kepler Mission as part of its 306 stars with planetary candidates are listed in the table below by designation number as a «Kepler Object of Interest» (KOI). (members.nova.org)
Eight years after Mike Brown of the California Institute of Technology in Pasadena discovered the object in 2002, he and his Caltech colleague Wesley Fraser used observations from the Hubble Space Telescope to estimate its diameter at some 890 kilometers. (sciencemag.org)
Those calculations yielded an estimated diameter of 250 kilometers or 150 miles across, large enough for the object to be classified as a protoplanet. (sciencedaily.com)