The easiest way is to sit down with a pitchpipe, keyboard, etc. (a MIDI editor would do) and work your way up and down a scale. (Be honest with yourself, though--growling is not singing low, and squeaking is not singing high.) If you're not trained and haven't warmed up, expect an octave to an octave and a half. If you're both, you might get two to three octaves. You'll probably also find that your range changes throughout the day. If you want to expand your range, do exercises and practice good vocal technique. Everyone does this differently, but there's some common advice: relax, and don't be uncomfortable enough to be tense, but maintain good posture. I was taught when sitting at rehearsal to use only the front third of my chair (forcing me to hold my back upright). It can be easier to just stand. Keep your head level, and push air up with your diaphragm instead of letting it slide out as you sing. As for the exercises themselves, simple scales will work. It's common to take five notes in a major scale and sing them in sequence, changing the key up or down by a half note each time. (For example, working up, you would sing C-D-E-F-G, then C#-D#-F-F#-G#, etc.) You can do this on a single syllable ("la") or take the opportunity to practice forming good vowel sounds ("la le li lo lu"). Similarly, lots of people get in some enunciation practice while warming up by singing a tongue twister on a single note, then repeating it faster and a half-note higher, then faster still and another half-note higher, until they trip over themselves or run out of notes. Whatever kind of exercise you choose, repeat it in one direction until you reach the end of your comfortable range, then try one or two more half-steps. Take a breather, then start again in the middle and do the same thing in the other direction. Over time, your limits will expand. Naturally, you should always take good care of your instrument. Drink a lot of water, take breaks when you need to, and stop doing anything that makes your chords feel stressed or otherwise painful. (Although the reasons aren't the same, it's analogous to any other kind of exercise: if you work too hard too often, you'll do more damage than good.) Avoid ice cold or boiling hot drinks before you sing, as well as milk. Good luck!