Imagine that the triangular shapes to the left represent shark teeth.  The triangles have been created so that if the one on the left measures 4 (slant length), then the one on the right measures 6 (slant length).  That's a 50% increase in slant length.  So why does the one on the right look at least 100% larger?  The answer is found in Geometry.

The area within a triangle (black area in this case) is calculated as follows.

Area = Base x Height / 2

Area = 4 x 4 / 2
= 16 / 2
= 8

Area = 6 x 6 / 2
= 36 / 2
= 18

You see, the size of the right triangle (area within)
actually IS more than double that of the left triangle.

And that's not even considering the fact that larger shark teeth are also thicker, making them heavier and more "beefy" feeling.

A relatively small increase in "slant length" can make a big increase in the apparent "size" of a tooth.  Below is a good example.
  

This is a graphic we use in our listings for the large Otodus obliquus teeth that we sell.  The tooth on the left is 2 1/4 inches - approximately the size of most medium-to-large Otodus teeth available in the market today.  The tooth on the right is 3 inches - approximately the size WE sell here at the web site.  The illustration is useful to explain how just 3/4 inch increase in "slant length" can create a significant increase in how large the tooth appears.