Rule of Nines

Article Author:
Ross Moore
Article Editor:
Bracken Burns
1/19/2019 3:54:31 PM
PubMed Link:
Rule of Nines


The Rule of Nines, also known as the Wallace Rule of Nines, is a tool used by trauma and emergency medicine providers to assess the total body surface area (TBSA) involved in burn patients.  Measurement of the initial burn surface area is important in estimating fluid resuscitation requirements since patients with severe burns will have massive fluid losses due to the removal of the skin barrier. This tool is only utilized for second-degree and third-degree burns (also referred to as partial thickness and full thickness burns) and aids the provider in quick assessment to determine the severity and intravenous fluid needs. Alterations to the Rule of Nines may be made based on body mass index (BMI) and age. The Rule of Nines has been shown to be the most frequently recited algorithm by physicians and nurses for estimating burn surface area in numerous studies.

The Rule of Nines estimation of body surface area burned is based on assigning percentages to different body areas. The entire head is estimated as 9% (4.5% for anterior and posterior). The entire trunk is estimated at 36% and can be further broken down into 18% for anterior compnents and 18% for the back. The anterior aspect of the trunk can further be divided into chest (9%) and abdomen (9%). The upper extremities total 18% and thus 9% for each upper extremity. Each upper extremity can further be divided into anterior (4.5%) and posterior (4.5%). The lower extremities are estimated at 36%, 18% for each lower extremity. Again this can be further divided into 9% for the anterior and 9% for the posterior aspect. The groin is estimated at 1%.


The Rule of Nines functions as a tool to assess second-degree and third-degree total body surface area (TBSA) in burn patients. Once the TBSA is determined and the patient is stabilized, fluid resuscitation may begin often with the use of a formula. Often the Parkland formula is used. It is calculated as 4 mL intravenous (IV) fluid per kilogram of ideal body weight per TBSA percent (expressed as a decimal) over 24 hours. Due to reports of over-resuscitation, other formulas have been proposed such as the Modified Brooke formula, that decrease the intravenous fluid to 2 mL instead of 4 mL. After the total volume of intravenous fluid resuscitation for the first 24 hours is established, the first half of the volume is given over the first 8 hours and the other half is given over the next 16 hours (this is converted to an hourly rate by dividing half the total volume by 8 and 16). The 24-hour volume time starts at the time of the burn. Should the patient present 2 hours after the burn and intravenous fluid resuscitation has not been started, the first half of the volume should be given in 6 hours with the remaining half of fluids running as per protocol. Fluid resuscitation is highly important in the initial management of second-degree and third-degree burns that encompass greater than 20% TBSA as complications of renal failure, myoglobinuria, hemoglobinuria, and multi-organ failure may arise if not aggressively treated early. Mortality has been shown to be higher in patients with greater than 20% TBSA burns that do not receive appropriate fluid resuscitation immediately following the injury.

Issues of Concern

There is a concern among clinicians of the accuracy of the Rule of Nines pertaining to the obese and pediatric populations. The Rule of Nines can be best used in patients greater than 10 kilograms and less than 80 kilograms if defined by BMI as less than obese. For infants and obese patients special consideration should be take as outlined below:

Obese Patients

  • Patients that are defined as obese by BMI have disproportionately large trunks compared to their non-obese counterparts.
  • Obese patients have a closer approximation to 50% TBSA of the trunk, 15% TBSA for each leg, 7% TBSA for each arm, and 6% TBSA for the head.
  • Android-shaped patients, defined as a preferential trunk and upper body distribution of adipose tissue (abdomen, chest, shoulders, and the nape of the neck), have a torso that is closer to 53% TBSA.
  • Gynecoid-shaped patients, defined as a preferential lower body distribution of adipose tissue (lower abdomen, pelvis, and thighs), have a torso that is closer to 48% TBSA.
  • As the degree of obesity increases, the degree of underestimation of truncal and leg TBSA burn involvement increases when adhering to the Rule of Nines.


  • Infants have proportionately larger heads which alters the surface area contribution of other major body segments.
  • A "Rule of Eights" better approximates infants weighing less than 10 kg." This rule dictates approximately 32% TBSA for the patient's trunk, 20% TBSA for the head, 16% TBSA for each leg, and 8% TBSA for each arm.

Despite the efficiency of the Rule of Nines and its penetrance into the surgical and emergency medicine specialties, studies show that at 25% TBSA, 30% TBSA, and 35% TBSA, percentage TBSA is overestimated by 20% when compared to computer-based applications. Overestimation of TBSA burned can lead to excessive intravenous fluid resuscitation giving the potential for volume overload and pulmonary edema with more cardiac demand. Patients with pre-existing comorbidities are at risk for acute cardiac and respiratory decompensation and should be monitored in the intensive care unit (ICU) during the aggressive fluid resuscitation phase, preferably in a burn center.

Clinical Significance

The Rule of Nines is a quick and easy tool used for the initial management of resuscitation in burn patients. Studies find that after examining the fully undressed patient, the percentage TBSA can be determined by the Rule of Nines within a few minutes.

Multiple studies found in a literature review stated that the patient's palm excluding the digits represented approximately 0.5% TBSA and that verification was noted with computer-based applications. The inclusion of the digits to the palm was found to be approximately 0.8% TBSA. The use of the palm, which is the basis for how the Rule of Nines was established, is found to be more appropriate for smaller second-degree and third-degree burns. It has been noted that the more training a specialist has, the less overestimation is present, especially on smaller burns.

Other Issues

Due to the inherent nature of the error in the human evaluation of burns even in the setting of rules, computer-based applications available for smartphones are being produced to minimize overestimating and underestimating TBSA percentages. The applications are utilizing standardized sizes of male and female models of small, average, and obese sizes. The applications are also moving towards measurements of infants. These computer applications are finding variability in the reporting of TBSA percentages by up to 60% overestimation of burn surface area down to 70% underestimation.

Intravenous fluid resuscitation guided by the Rule of Nines stands only for patients that have greater than 20% TBSA, and these patients should be transported to the nearest trauma center. Except for special areas, such as the face, genitals, and hands, that need to be seen by a specialist, transfer to major trauma centers are only necessary for greater than 20% TBSA burns. The American Burn Association (ABA) also has defined criteria of which patients should be transferred to a burn center.

Once fluid resuscitation has been initiated, it is important to identify if appropriate perfusion, hydration, and renal function are present. The resuscitation derived from the Rule of Nines and intravenous fluid formula (Parkland, Modified Brooke, among others) should be closely monitored and adjusted as these initial values are guidelines. The management of severe burns is a fluid process requiring constant monitoring and alterations. Lack of attention to details can result in higher morbidity and mortality as these patients are critically ill.


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