The truth is, with women's heels, many don't give what you might imagine. Its all to do with the pivot point of your foot. If you measure yourself barefoot and then go on your tip-toes, you'll probably find you can get close to 3 inches of height. So to get 4 inches of actual height you need a high angle shoe and a platform at the front that is at least 1 inch.
Here is a video talking about heel height in more detail...and also below this video are examples of how much actual height each type of heel size gives the average ladies foot.