Rule of Nines

Category: Concepts Sources: raw/protocols/nm-sop-guidelines-treatment-2022.pdf Last updated: 2026-04-05

Overview

The Rule of Nines is a method for estimating total body surface area (TBSA) involved in a burn injury. TBSA percentage drives three critical prehospital decisions: whether to call for ALS and IV fluid resuscitation, whether to transport to a burn center, and how to calculate fluid replacement using the Parkland formula.

The Rule of Nines divides the adult body into regions, each representing approximately 9% (or a multiple of 9%) of total surface area. It is fast enough to use at the bedside or in the back of the ambulance. It is not precise — precision is the job of the burn center's Lund-Browder chart — but it is accurate enough for prehospital triage.

Only partial and full-thickness burns are counted in TBSA. Superficial (first-degree) burns — redness only, no blistering — are excluded from the calculation.

Adult Rule of Nines

Body Region	TBSA %
Head and neck	9%
Each upper extremity (arm)	9% each
Anterior trunk (chest)	9%
Anterior trunk (abdomen)	9%
Posterior trunk (upper back)	9%
Posterior trunk (lower back/buttocks)	9%
Each lower extremity (thigh)	9% each
Each lower extremity (lower leg/foot)	9% each
Perineum / genitalia	1%
Total	100%

Simplified adult breakdown: - Head: 9% - Each arm: 9% (both arms = 18%) - Front of torso: 18% (chest 9% + abdomen 9%) - Back of torso: 18% (upper 9% + lower/buttocks 9%) - Each leg: 18% (thigh 9% + lower leg/foot 9%) → (both legs = 36%) - Perineum: 1%

Memory check: 9 + 9 + 9 + 18 + 18 + 18 + 18 + 1 = 100%

Worked Example

A patient has burns covering: - Entire right arm (9%) - Anterior chest (9%) - Anterior abdomen (9%)

Total TBSA = 27%

This patient has a critical burn (>20% TBSA partial thickness), requires ALS IV access, Parkland formula fluid resuscitation, and burn center transport.

Pediatric Modifications

Children are not small adults when it comes to burn TBSA. The pediatric head is proportionally larger than the adult head, and the legs are proportionally smaller. Using adult Rule of Nines on a child systematically underestimates head burns and overestimates leg burns.

General rule: - Head: up to 18% in infants (decreases with age toward adult 9%) - Each leg: approximately 14% in infants (increases with age toward adult 18%) - Trunk: relatively consistent with adult proportions

Lund-Browder chart is the accurate pediatric TBSA tool — it adjusts head and leg percentages by age in years. In the field, use the palm method (below) for small or irregular pediatric burns, and acknowledge that your TBSA estimate is approximate. Notify the receiving facility that the patient is pediatric and burn center transport decisions should account for age-adjusted TBSA.

The Palm Method

Patient's palm (fingers together, not spread) = approximately 1% TBSA

Use this for: - Scattered or irregular burns that don't fit neatly into Rule of Nines regions - Small burns where you want to confirm the burn is below or above a threshold - Rapid rough check when the exact Rule of Nines breakdown is unclear

Important: Use the patient's palm, not your own. An EMT with large hands on a child would dramatically overestimate.

NM Protocol note: NM EMS Treatment Guidelines explicitly state: "TBSA quick method: patient's hand = 1% TBSA."

Combining the methods: For a patient with scattered burns across multiple regions, you can estimate each patch using the palm method and sum them, or use Rule of Nines for large continuous burns and palm method for outlier patches.

Critical Burn Thresholds

The following criteria define a critical burn requiring burn center transport:

Criterion	TBSA / Specifics
Partial thickness burns	>20% TBSA
Any full-thickness burn	Any TBSA
Facial burns / airway involvement	Singed nasal hair, soot in nares, stridor, hoarseness
Burns to hands, feet, genitalia	Any TBSA — functional impact
Circumferential burns	Any extremity or torso — compartment syndrome / respiratory restriction
Chemical burns	Any significant exposure
Electrical burns	Any — internal injury cannot be assessed by TBSA alone
Burns + concurrent trauma	Compound severity
Extremes of age or significant comorbidities	Any burn becomes more critical

Airway burns are a special case: they are not assessed by TBSA but by mechanism (enclosed space, facial burns, inhalation of hot gases or smoke) and findings (singed nasal hair, soot in the airway, hoarseness, stridor). Airway edema from inhalation injury can develop rapidly — early airway management before obstruction is critical, even if TBSA is small.

Parkland Formula — Fluid Resuscitation

The Parkland formula calculates fluid resuscitation volume for burns exceeding 20% TBSA. This is ALS scope — EMT-B establishes IV access; fluid administration is ordered and titrated by ALS or the receiving burn center.

Formula:

4 mL × body weight (kg) × %TBSA = total fluid volume for first 24 hours

Fluid of choice: Lactated Ringer's (LR)

Timing: - Half of total volume given in the first 8 hours from time of injury (not time of first IV) - Remaining half given over the next 16 hours

Field calculation (quick method):

Body weight (kg) × %TBSA = mL of LR in the first 2 hours

This gives a rough early-phase target for the first hours of resuscitation — useful during transport.

Worked Example

70 kg adult with 30% TBSA burns: - Total 24-hr volume: 4 × 70 × 30 = 8,400 mL LR - First 8 hours (from injury): 4,200 mL - Next 16 hours: 4,200 mL

Why this matters prehospital: You won't be calculating Parkland formula for the full 24 hours. But knowing the formula tells you whether this patient needs large-bore IV access immediately and ALS intercept. A patient with 30% TBSA burns who has waited 2 hours before EMS arrival is already significantly behind on fluid resuscitation.

Documentation

Burn documentation on the PCR should include: - Burn depth at each location (superficial/partial/full thickness) - Estimated TBSA (and which method used — Rule of Nines or palm) - Location (note face, hands, feet, genitalia, circumferential) - Evidence of inhalation injury (singed hair, soot, stridor, SpO2) - Time of injury (Parkland formula starts from this time, not transport time) - Burn center transport if criteria met; Medical Control notification

Common Mistakes

• Including superficial (first-degree) burns in TBSA — Redness from a sunburn or minor flash burn is not counted. Only partial and full thickness burns go into TBSA. Including superficial burns will overestimate TBSA and may lead to over-aggressive fluid resuscitation.
• Using adult Rule of Nines for pediatric patients — The head and legs are different proportions in children. Use the palm method for children, or acknowledge the approximation and consult the receiving facility.
• Forgetting the perineum — The 1% perineum is often omitted in quick calculations. It is also a critical burn location (automatic burn center criteria) regardless of TBSA.
• Applying the Parkland formula from transport time instead of injury time — If a patient was burned 2 hours ago and you're now initiating IV resuscitation, the "first 8 hours" clock started at the time of injury. The receiving burn center needs the injury time to recalculate the schedule.
• Measuring TBSA on all burn depth — Again: superficial burns do not count. Partial and full thickness only.
• Using your own palm to estimate 1% TBSA — Use the patient's palm. Your palm on a pediatric patient is not 1% of their TBSA.

NM Protocol Notes

From NM EMS Treatment Guidelines (2022), Thermal Burns — EMT-B scope:

• Estimate % BSA affected; distinguish partial vs. full thickness
• TBSA quick method: patient's hand = 1% TBSA
• For burns >20% BSA: second IV in unburned area; Parkland Formula calculation
• 4 mL/kg/TBSA = mL for first 24 hours
• Half in first 8 hours; half over next 16 hours
• Quick field calculation: weight (kg) × TBSA = mL in first 2 hours
• LR is the preferred fluid (not normal saline — large NS volumes worsen hyperchloremic acidosis)
• Transport to appropriate facility; contact Medical Control for burn center destination decision
• Air evacuation consideration for critical burns in rural San Juan County — Farmington to the nearest burn center is a significant distance; early helicopter request is appropriate

NREMT Relevance

High-yield topic on the cognitive exam:

• Know the adult Rule of Nines — memorize percentages for each body region
• Know the palm method: patient's palm = ~1% TBSA
• Know what is NOT included in TBSA: superficial (first-degree) burns
• Know critical burn thresholds: >20% TBSA partial thickness; any full thickness; airway burns; face/hands/feet/genitalia
• Know the Parkland formula: 4 mL/kg/% TBSA; half in first 8 hours
• Know that pediatric TBSA estimation differs from adult (larger head, smaller legs)
• Airway burns are assessed clinically (singed hair, soot, stridor), not by TBSA

Related

• burns — clinical management of burns; depth classification; airway burn management; transport decisions
• rule-of-nines — this article (self-referencing for internal consistency)
• secondary-assessment — DCAP-BTLS B component; burns documented during physical exam
• shock-physiology — large TBSA burns cause hypovolemic shock via plasma loss into damaged tissue
• bleeding-control-shock — fluid resuscitation and shock management principles

Sources

• raw/protocols/nm-sop-guidelines-treatment-2022.pdf — Burns Thermal (p. 64–65)