How wide is the sun?
The Sun is 875,000 miles across, though scientists usually use kilometers, in which case it is 1,392,000 kilometers across. It is also very heavy. To write its weight in kilograms (1kg = 2 pounds, more or less) you write 2 followed by 30 zeros!
how much does the sun weigh?
The Sun is about 2,000,000,000,000,000,000,000,000,000,000 kg (a 2 with 30 zeros kg, or about 4.4 with 30 zeros lbs). Maybe you learned in your physics class what's the difference between weight and mass. For example a person of 50 kg weighs 50 kg on Earth, 8.3 on the moon, and 1354 on the Sun.
How big around is the Sun?
The radius of the Sun is about 700,000 km (435,000 miles). As you know the circumference of a circle is 2 pi r, where r is the radius. That makes 4.4 million kilometers (2.7 million miles) for the circumference. For comparison, the circumference of the Earth is about 40,000 km (25,000 miles), about 100 times smaller than the Sun.
How heavy is the sun?
The Sun has a mass of 2*10^30 kg, that is about 300,000 times greater than the mass of the Earth. Mass depends on the amount of matter in an object. Weight on the other hand, varies with respect to local gravity, however the Sun is not sitting near anyones gravitational field.
How many of earth's moon would fit inside the sun if it were hollow? ?
Well, the radius of the moon is about 1,080 miles, and the radius of the Sun is about 432,687 miles. The moon and the sun are both spheres, and math tells us how to relate the volume inside a sphere to its radius. I don't know how much math you have done, so let me just tell you the answer and you can maybe ask your teacher for more information. The answer is that you could get about 64.3 million moons inside the Sun if it were hollow.
How many saturn's could you fit inside the sun?
Almost 1600 Saturns would fit inside the Sun.
How many pluto's could fit inside the sun?
This answer even surprised me. 250 million plutos would fit inside the Sun.
How do you determine the size of the Sun? Is our Sun the biggest?
We know the 'angular' size of the Sun - how big it is looks to be on the sky - in degrees (it's about half a degree). We can convert that into a physical size for how big it is in miles or kilometers, only by knowing how far away it is. (for example, the moon and the sun look about the same size to us on Earth but the moon is much closer so it must be smaller) If you multiply the angular size (in radians, which is another unit of angle) by the distance then you get the diameter.
How far away the Sun is is determined by a couple of methods. One is a direct measurement of its distance by bouncing a radio wave off it (radar), but this is not such a good method as the Sun's outer atmosphere scatters the waves. So the more reliable method is to combine what we know about the way the Sun's gravity makes planets move (Kepler's Laws of planetary motion), with observations of the planets' movements and radar measurements of distances to the planets, to work out the distance to the Sun. This is an indirect way of getting the distance but very accurate since it is easier to measure the distance to a planet with radar, and there are several planets which you can usefully use to make independent calculations.
The Sun is not the biggest star! There are stars called red giants (like Betelgeuse in the constellation of Orion) which have diameters 10 to 40 times the size of the Sun. But it is also not the smallest. Stars with diameters only one tenth of the Sun also exist.