How much of an atom is empty space?

Atoms are almost entirely empty space. A hydrogen atom is about 100,000 times wider than its nucleus; scale the nucleus up to a football and the electron would be several kilometres away. Compress all 8 billion humans to nuclear density and they would occupy about 2 cubic centimetres, the size of a sugar cube.

Source: Standard atomic physics (nuclear density about 2 × 10¹⁷ kg/m³)