A simple equation to calculate the diameters of biological vesicles
  The remarkable preference of biomembranes, to constitute vesicles of certain discrete sizes is explained by using the following properties of phospholipids that are either well understood or at least documented.   A. By hexagonal close-packing their fatty acyl chains form a triangular lattice.   Their molecules:   B. Prefer to form linear arrays that occasionally make angles of 120 degrees.   C. Form relatively large hexagons. Based on these properties a model for monolayers is proposed and a simple equation derived for the calculation of diameters of vesicles. The diameters of vesicles of neurotransmitters and hormones determined by electron microscopy were compared with those obtained with the equation. Statistical analysis of this comparison revealed the model to give very significant results (p=.0002). 
Willy S. Bont