What does this number measure?
A compact stellar remnant with extreme densities. A neutron star can form after the collapse of a massive star's core. A diameter of a few tens of kilometres is a model reference, not a measurement valid for all such objects.
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.
Neutron star: conceptual interpretation of the compact disc; illustrative texture, colour and hot spots, model diameter.