Stars come in huge range of different sizes. Neutron stars can be just 20 to 40 km in diameter, whereas white dwarf can be very similar in size to Earth's. The largest supergiants, on the other hand, can be more than 1500 times larger than our Sun. With the Sun having a radius of 695,000 km, this means that in the extreme cases, we are looking at a star of over 1,000,000,000 km.
However, because supergiants are overly bloated stars in the final stages of their lifetime, they are far less concentrated (or dense) than a typical sun-like star, and so wouldn't actually weigh a great deal more than the Sun. Indeed, the famous red giant, Betelgeuse, is about 1000 times larger than the Sun, and yet only weighs about 15 times as much. With the atmospheres of large stars being so spread out, they tend to be a lot cooler and redder than a typical mid-life star.