This is an interesting question. We know about the Universe, but not enough to answer all its questions. In our Solar System the Sun is the biggest star. Considering that there are millions of galaxies apart from ours, there are also millions of stars, bigger and smaller than our Sun. Astronomers don't know how big the biggest star in the universe is, but one astronomer says he has a rough idea. The largest gaseous ball may be about 130 times more massive than our sun. There is the scientific classification of stars according to their size, and they are measured according to our suns size.

Super giants are the largest stars, and may have diameters several hundred times the size of the Sun.

Giants are more common than Super giants, and have diameters 10 to 100 times as large as the Sun.

Red Giants have cooler temperatures than giants, and are thus less bright, but their size is still massive.

Medium-size or dwarf stars are about as large as the sun.

White dwarfs are small stars (smaller than the distance across Asia).