Mastering the Rule of 9s: A Comprehensive Guide for Adult Burn Assessment in Next Generation NCLEX Review

The Rule of 9s helps nurses determine what percentage of total body surface area is affected by burns.

Knowing this rule is a quintessential part of your job as a nurse, and an essential tool in high-pressure situations. It’s also especially important for you to know it if you want to pass the Next Generation NCLEX with flying colors.

Which is why, in this week’s episode of NCLEX Ready, I break down everything (and I mean everything) you need to know about the Rule of 9s.

Are you ready?

Let’s dive in!

What Is the Rule of 9s?

The Rule of 9s is an essential tool to evaluate burn victims by healthcare professionals. Assessing the burn injuries is essential to be able to provide immediate intervention. Nursing students have experienced answering questions on their exams at some point in nursing to demonstrate the understanding of the Rule of 9s.

But why do nurses need to know the total body surface area percentage burned?

Simply because we need to know the severity of the burn so we can decide what fluid treatment is needed, especially during the initial 24 to 48 hours for moderate to severe burns. Lactated Ringer’s solution is commonly the fluid of choice.

To understand the Rule of 9s, you must remember the percentage of each body section.

Below is a breakdown of how the Rule of 9s divides the body into sections:

Let’s Go Over Some Scenarios Together

If only the right front leg has sustained burns, then this is considered 9% of the total body surface area (TBSA). If the right front and back leg has sustained burns, then this is considered 18% of the total body surface area.

Keep in mind that the entire head and neck makes up 9%. The front of the head is 4.5% and the back of the head is 4.5% of the total body surface area.

Each arm makes up 9% each. So if just the front of one arm has burns, then this area makes up 4.5% of the total body surface area.

The entire torso makes up 36% of the body. The anterior trunk makes up 18% and the posterior trunk makes up 18%. If half of the anterior trunk has sustained burns, then this is 9% of the total body surface area.

Each leg makes up 18% of the body. If both legs have sustained burns, then that would be a total of 36% of the total body surface area. If just the right front leg has sustained burns, then this would equate to 9% of the total body surface area.

Then the perineum area makes up 1% of the total body surface area.

Let’s Answer Some Rule of 9s NCLEX Questions

Question #1

Nurse Camille is providing care for a 30-year-old male patient who has been brought to the Emergency Department after sustaining burns from a house fire. The nurse noted that the patient has full-thickness burns on the front of the right leg and the entire right arm. Using the Rule of 9s, what percentage of the patient’s total body surface area is affected by burns?

1. 18%
2. 36%
3. 45%
4. 24.5%

Answer: 18%.

Rationale: According to the Rule of 9s in adults, the front of a leg accounts for 9% of the total body surface area. The entire right arm accounts for 9% of the total body surface area. Adding 9% and 9% together results in the total body surface area affected by burns in this patient to be 18%. 

Question #2

Nurse Goku is providing care for a 25-year-old female patient who has sustained third-degree burns on the front of her torso and the entire left arm. The nurse will use the Rule of 9s to calculate the percentage of the total body surface area affected. Which of the following is the correct answer?

1. 18%
2. 27%
3. 36%
4. 45%

Answer: 27%.

Rationale: According to the Rule of 9s in adults, the front of the torso is 18% and the entire left arm is 9% of the total body surface area. Adding 18% and 9% together results in the total body surface area affected by burns on this patient to be 27%. 

Question #3

Nurse Luffy is providing care for a 36-year-old male patient who has sustained burns on both legs and the perineum. The nurse will use the Rule of 9s to calculate the percentage of the total body surface area affected. Which of the following is the correct answer?

1. 18%
2. 19%
3. 36%
4. 37%

Answer: 37%.

Rationale: According to the Rule of 9s in adults, each leg represents 18% and the perineum represents 1% of the total body surface area. 

18% + 18% + 1% = 37% of the total body surface area.

Question #4

Nurse Naruto is providing care for a 45-years-old female patient who has sustained burns on both arms and the entire right leg. Calculate the percentage of the patient’s total body surface area affected by burns according to the Rule of 9s.

[Fill in the blank with the right answer.

Answer: 36%.

Rationale: By now, you are a pro at calculating the total body surface area affected by burns using the Rule of 9s, so we don’t need multiple choices anymore. Not to mention, this is the perfect scenario for the NCLEX to provide you with a fill-in-the-blank question! 

According to the Rule of 9s in adults, each arm represents 9%, which totals 18%. Each leg represents 18% and in this scenario, only the right leg is affected. 

18% + 18% = 36%.

Question #5

Nurse Grey is providing care for a 50-year-old male patient who has sustained burns on the front right arm, the entire back torso, the entire front torso, the back of the head, and the genitalia area. Calculate the percentage of the patient’s total body surface area affected by burns according to the Rule of 9s.

[Fill in the blank with the right answer.]

Answer: 46%.

Rationale: The front right arm makes up 4.5%, the entire back torso makes up 18%, the entire front torso makes up 18%, the back of the head makes up 4.5%, and the genitalia area makes up 1%. 

4.5% + 18% + 18% + 4.5% + 1% = 46% of the total body surface area.