Easiest way to know for sure is to lift both rear tires off the ground and put the axle on jack stands. With it properly secured (blocks on the front tires) get underneath. Turn the driveshaft and make sure both tires are turning the same direction at the same speed.
Mark one of the tires. Turn the driveshaft, counting how many times you have to turn it to get the tires to make one complete rotation.
3-1/4 => 3.21
3-3/4 => 3.73
Just over 4 => 4.10
4-1/2 => 4.56
Almost 5 => 4.88
Just over 5 => 5.13
All the rotation counts are approximate.