The factor of subdivision introduces a safety measure by reducing the size of the compartments to limit the effects of flooding. It ensures that the ship's draft or trim has less chance of touching the margin line during flooding or heeling.

Permissible Length Formula:

$$Permissible\:length=\frac{Floodable\:length}{Factor\:of\:Subdivision}$$

A smaller factor of subdivision leads to a smaller permissible length, requiring more numerous and smaller compartments. This reduces the potential for catastrophic flooding, as a smaller flooded area is less likely to exceed the ship's reserve buoyancy and cause it to sink. The factor of subdivision is determined by the ship's length and its intended service. The nature of service is quantified by a "criterion of service" (Cs) number, which considers the proportion of passenger and machinery spaces to the total volume of the ship. A higher Cs number (indicating more passenger space) typically results in a lower factor of subdivision and therefore smaller compartments.