Easiest way is look on the ring gear. It is stamped with the ratio.
If you don't want to remove the pumpkin, you can make a chalk mark on the tire and a chalk mark on the drive shaft. Turn the tire through one revolution and count how many times the driveshaft spins through it's cycle
Ex: If the tire is turned one full turn and the drive shaft turns 3 full turns then the ratio would be 3.00. Make sense?
Not as accurate, but will get you a ballpark number.
Steve