The rule of nines is used to estimate the percentage of body area that is burned on an adult using multiples of nine, according to eMedicineHealth. This percentage is used to decide treatment options, such as fluid resuscitation or transfer to a burn unit.
The percentage for each body part is as follows: 4.5 percent for the head and each arm, 9 percent for the front chest, the back chest, the front abdomen, the back abdomen and each leg, and 1 percent for the groin area. These percentages are added together to find the total percent of surface area affected by the burn. For example, if the front abdomen, one arm and one leg are affected, the total surface area affected totals 9 percent plus 4.5 percent plus 9 percent, or 22.5 percent.