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!
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.
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.
The Sun has a mass of 2*10^30 kg, which 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 anyone's gravitational field.