The sun is 1,392,000 km in diameter. That’s over 100 times the diameter of the earth, and you could fit well over a million Earths inside.
But in about 5 billion years time, it will expand to twice its current size to become a red giant, probably consuming the Earth and burning it to a crisp. But don’t worry, humans will probably be long gone – extinct or travelling the universe, by then!
The sun is quite big, like Leila, Adam, and Catherine have said: I would have said 1,600,000 km diameter compared to 12,800 km for the Earth.
But the sun is quite a middle-sized star. The smallest stars, ignoring the really odd ones like black holes or neutron stars, are about the size of the Earth. The biggest stars like Betelgeuse (pronounced ‘Beatle Juice’) are huge, nearly 1,000,000,000 km in diameter or 100,000 times the size of the Earth.