Can you explain how 5X100 and 5X114.3 are different?

ie if the rim doesn't have any markings.. how would one tell if its 100 or 114? where are the measurements taken from?

The 5x100 and 5x114.3 is the bolt pattern of the wheel, if you dont know what that is picture a circle with those diameters and and center of each lug will line up on that circle.
If the wheel isn't marked the easiest way to check is to measure the distance between the center of two adjacent holes, knowing the number of holes its simple math to figure out the diameter, for a 5x100 adjacent holes would be 58.78mm(2.31in) apart and for 5x114.3 it would be 67.18mm(2.64in). A ruler is accurate enough to know the difference between these two examples but if you have a pair of dial calipers measure the closest points of the adjacent hole then just subtract the diameter of the hole from the numbers I gave you.
Its a little wordy but I hope it helps

Thanks Fuzzy much appreciated.. May be a silly question but would this (58.78mm and 67.18mm) also apply to 4X100 and 4X114.3?

For a 4 lug setup the 58mm and 67mm wouldn't be right, but for an even number of lugs its a lot easier to measure. Just measure straight across the bolt pattern to get the bolt pattern diameter, ie 4x100 would be 100mm between the lugs straight across the center from each other.

Danke!

good info