How can I find out what my singing/vocal range is?

The best way is to use a piano, or any other instrument on which you can play the notes of at list three octaves - the middle one, the one before it and the one after it. But you better find someone to play for you, cause basic singing only up and down the notes is not gonna do the trick. You will need to do some exercises with your voice in oreder to reach your top and your bottom. You know, like c-d-e-d-c, then go up d-e-#f-e-d, and more steps up, then go down, then up again, them some with skipping notes (the notes of a cord only).... all this in order to strech your voice before reaching your extremes. You will never see your vocal range by simple singing down from middle C and then up from it. All the muscles included in producing a voice need waking up first, and excercising before becoming ready for the activity.... in fact that's the case for any muscle and any activity we do :) and yeah.... see that you check your vocal range more then five hours after you've woken up.