[big gear head]

The best way is to remove the cover and count the teeth on the ring gear and pinion. There are other less accurate ways. If it has a standard differential then you can raise one wheel off the ground and turn the wheel exactly 2 full turns. Count the number of times the drive shaft turns. If it turns 3 1/3 times then it's a 3.36. If it turns just over 3 times then it's a 3.08. If it turns 2 3/4 times it's a 2.73...... If it has a limited slip differential then raise both wheels off the ground and turn them exactly 1 turn and count the times the drive shaft turns. Both wheels must turn exactly 1 turn.