Here's a few combined copy and pastes from NASA, High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center......
The Solar System has been measured to be about 28,000 light years from the center of the galaxy, and about 20 light years above the galaxy's equatorial plane. It is within the "Orion" spiral arm.
The disk of the Milky Way galaxy is about 100,000 light years in diameter (one light year is about 9.5 x 1015 meters), but only about 1000 light years thick. Our Galaxy contains about 200 billion stars. Most of the stars are located in the disk of our galaxy, which is the site of most of the star formation because it contains lots of gas and dust.
So.......When we ask how far are we from the center of the galaxy, or how large our galaxy is, we do know the real answers for these questions =)