Burn Surface Area Calculator: Uses & Formula

This burn surface area calculator estimates the percentage of total body surface area (TBSA) affected by a burn. You enter the patient’s age group and the body regions burned, and the calculator returns the estimated TBSA percentage using the Rule of Nines or the Lund-Browder chart, depending on the method you select. The result is a crucial first step in guiding fluid resuscitation and determining whether transfer to a burn center is needed.

Formula

The Rule of Nines assigns fixed percentages to major body regions in adults:

• Head and neck: 9%
• Each entire arm: 9% (front and back combined)
• Anterior trunk: 18%
• Posterior trunk: 18%
• Each entire leg: 18%
• Perineum: 1%

Total TBSA = head + left arm + right arm + anterior trunk + posterior trunk + left leg + right leg + perineum (if burned). The perineum is not included in the calculator inputs because it is a small, fixed 1% that is often overlooked; add it manually if burned.

For children, the head is proportionally larger and the legs smaller. The Lund-Browder chart adjusts these percentages by age. A common pediatric modification is: head = 9% + (age in years − 1) × 0.5%, and each leg = 18% − (age − 1) × 0.5%. This calculator uses a simplified version: for children under 10, head = 14% and each leg = 14% (approximate values for a 5-year-old). For accuracy, use a full Lund-Browder chart for children under 10.

Worked Example

Using the default values: an adult with burns on the head (9%), left arm (9%), right arm (9%), anterior trunk (18%), posterior trunk (18%), left leg (18%), and right leg (18%) – that is, the entire body surface burned.

Total TBSA = 9 + 9 + 9 + 18 + 18 + 18 + 18 = 99%.

The calculator shows 99.0% (the perineum is not included). This matches the Rule of Nines total of 99% (the 1% perineum would make 100%).

When to Use This Calculator

This tool is for initial assessment in an emergency or clinical setting. It is not a substitute for professional medical evaluation. Use it to:

• Estimate burn size for fluid resuscitation (Parkland formula: 4 mL × weight in kg × %TBSA over 24 hours).
• Determine if the burn meets criteria for transfer to a burn center (e.g., >10% TBSA in children, >15% in adults).
• Document the extent of injury for medical records.

Only partial-thickness (second-degree) and full-thickness (third-degree) burns are counted. First-degree burns (like sunburn) are not included because they do not cause significant fluid loss.

How to Read the Result

The result is a percentage of total body surface area. For example, a 20% TBSA burn in an adult is considered major and requires IV fluids. In children, a 10% burn is similarly significant. The percentage directly influences the Parkland formula: for a 70 kg adult with 20% TBSA, the first 24-hour fluid requirement is 4 × 70 × 20 = 5600 mL, with half given in the first 8 hours.

Remember that this is an estimate. The actual burn area may be smaller if the burn is patchy, or larger if the patient is obese (the Rule of Nines overestimates in obese individuals because body proportions change).

Common Mistakes and Limitations

• Including first-degree burns: Only second-degree and deeper burns count. Sunburn is not included.
• Using adult percentages for children: Children have proportionally larger heads and smaller legs. Use the pediatric adjustment.
• Forgetting the perineum: It is 1% and often overlooked, but it matters for small burns.
• Estimating irregular burns: For scattered burns, use the patient’s palm (approximately 1% TBSA) to estimate the total area.
• Overestimating in obese patients: The Rule of Nines assumes standard body proportions, which may not hold for very large or very small individuals.

Alternatives to the Rule of Nines

The Lund-Browder chart is more accurate for children and adjusts for age. The Palmer method (patient’s palm = 1% TBSA) is useful for small or irregular burns. For very large burns, some clinicians use the “rule of fives” or computer-assisted planimetry, but these are less common in the field.

Frequently Asked Questions

Do I count blistered skin as a burn?

Yes, blistered skin indicates a second-degree burn and should be counted. Only first-degree (red, painful, no blister) burns are excluded.

How accurate is the Rule of Nines?

It is a rapid estimate, accurate to within about 5% for adults with standard body proportions. For children, the Lund-Browder chart is more accurate. It is not a precise measurement, but it is sufficient for initial management.

What is the Parkland formula?

The Parkland formula calculates fluid needs for burn patients in the first 24 hours: 4 mL × body weight in kg × %TBSA. Half is given in the first 8 hours, and the rest over the next 16 hours. This calculator gives the %TBSA you need for that formula.

Can I use this calculator for a child?

Yes, but the result is only approximate. The calculator uses a simplified pediatric adjustment (head and legs = 14% each). For precise pediatric values, use a Lund-Browder chart or consult a burn specialist.

What does “partial thickness” mean?

Partial-thickness burns (second-degree) involve the epidermis and part of the dermis. They cause blisters and pain. Full-thickness burns (third-degree) destroy all skin layers and may be painless due to nerve damage. Both are counted in TBSA.

Is this calculator a substitute for a doctor?

No. It is an educational and initial assessment tool. Any burn larger than 10% TBSA in a child or 15% in an adult, or involving the face, hands, genitals, or joints, requires immediate medical attention.

Related

• Permutation Calculation Steps and Formula
• Percent Change Calculation Equation and Examples
• Hypotenuse Calculation Steps and Formula

in age | Age group | - | Adult=1, Child=2 | 0
in head | Head | % | 9 | 0
in arm_l | Left arm | % | 9 | 0
in arm_r | Right arm | % | 9 | 0
in chest | Anterior trunk | % | 18 | 0
in back | Posterior trunk | % | 18 | 0
in leg_l | Left leg | % | 18 | 0
in leg_r | Right leg | % | 18 | 0
out tbsa | Total TBSA | % | head + arm_l + arm_r + chest + back + leg_l + leg_r | 1
out rule_nines | Rule of Nines check | % | 9 + 9 + 9 + 18 + 18 + 18 + 18 | 0