What does this number measure?
A white dwarf with dimensions close to Earth's. Sirius B is the compact companion of Sirius A. It concentrates a stellar mass into a much smaller volume; its surface appearance is interpreted here.
Compare the stated dimensions
The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.
Source and limitations
Catalogue order of magnitude; a source is provided, but this measurement has not been individually audited.
Sirius B, a compact white dwarf: interpreted disc and surface, without a resolved photograph of that surface.