Our Sun is more than 1.4 million km across. But stars are not all the same size. They range from the size of a city, to large enough to swallow half our Solar System!
Neutron stars pack a lot of mass into a small volume. They may contain the mass of one or two Suns but are often just 20 to 40 km in diameter. White dwarf stars are a bit bigger - often similar in size to our planet Earth.
The largest supergiant stars can be more than 1500 times larger than our Sun. This makes them over 2,000 million km across. However, supergiants actually don't contain thousands times more mass than the Sun. This is because supergiants have expanded as they age, so all the stuff inside them is much more spread out. The red giant, in the constellation of Orion, Betelgeuse, is about 1000 wider larger than the Sun but only contains about 15 times as much mass.