How big is our galaxy?

Answer

Our own galaxy, the Milky Way, is a flat disk of stars, dust and gas. Around it is another spherical whole with here and there a few groups of stars. The whole is about 100,000 light-years in diameter. A light year is a distance of just under 9.5 million million kilometres, that is 9.5 trillion or 9 500 000 000 000 kilometres.
The diameter of the Milky Way is then 950 000 000 000 000 000 kilometers. The disk of the Milky Way is thinner: 12,000 light-years, but that’s still 114 000 000 000 000 000 kilometers!
There are 200 billion stars in the Milky Way, maybe even 400 billion, because astronomers don’t yet know how many small stars there are.