Do you mean the length of the wire connecting the needles? Yes, there are different lengths. I'm knitting now on a 16 inch and a 32 inch. I think there are 12 inch needles but all the hat patterns I've seen use double pointed needles.
Most people use 16" long needles (that's measured tip to tip, not just the cord), but I do hats on a 24" and use a one loop variation of the magic loop. You could try that one, or the full on Magic loop, no need to buy another needle.