Speaker wire length?

I'm not an audio nut, but I can get some by-the-foot aftermarket wire for cheap and it should be a good way for me to improve the sound of my stereo. So does anyone know off hand what the total length of speaker that wire runs through the cabin of a hatchback? Or how many feet are needed to do the job? Also should I get 16 ga wire, its just for a middle of the road Pioneer unit (circa 2004).
 
If you are just running a head unit without any external amps, I'd say save yourself the trouble and leave the stock wiring how it is. If you were using an amplifier to power the speakers and/or subwoofers, I'd say then it would be necessary to get full sound from those components.
 
I'm only considering doing it because I can buy nice by-the-foot wire like the spiral type for well under a buck from my job. Also the stock speaker wiring in my drivers door is shorted out, so when I close the door the speaker doesnt work, open the door and theres sound, so I have a reason to do it. Right now I have it bypassed with some cheapo wire; maybe I'll just see what $20 worth or wire will get me.