For the best appearance, there is a preper size proportion between the base and the height. That is approximately 2. That is the base should be about twice the size of the height; anywhere from 1.85 to 2.15 depending on the height. The differences show up more in taller tiaras. Here, "base" means the width of the tiara from left to right at the widest point and height measures from the bottom to the apex or tallest points if there are more than one apex as in the "butterfly tiara [:LEARN MORE].
Now all this calculator does is multiply. That may not be much of a help if your base is, say, 4 and you want the height. 4x.5=2. but what if the base is 5.75? or what if the height is 2.43 and you want the base? or what if you have a base of 4.34 and you want all the useful heights so you want to calculate the base times each figure from .48 to .52?
So the rule is: If you know the height then the base is h x about 2. If you know the base then the height is b x about .5.