This calculator gives an indication of how a boat will ride. The ideal result is 64. A boat with that heave/comfort factor will have a natural feel in the water. Boats with higher factors will tend to feel heavy and sluggish while boats with smaller factors will tend to be light and bouncy.
The waterline area factor is an approximation. If you know the percentage of your waterline area in relation to the area of a rectangle with waterline length times waterline beam, you can edit that box with your number.