A single teaspoon (or sugar cube) of neutron-star material would weigh roughly a billion tons on Earth — about as much as a mountain. NASA puts it at ~1 billion tons per sugar cube, while other sources cite up to 6 billion tons per teaspoon. The reason is that a neutron star packs more mass than the Sun into a sphere only about 20 km (12 miles) across.

chandra.harvard.edu