The Rule of 9's is a fast way to estimate the percentage of the body burned — the Total Body Surface Area (TBSA). You need that number for one reason: it is the input to the fluid-resuscitation formula. Once you have TBSA, the Parkland formula tells you how many milliliters of Lactated Ringer's to give in the first 24 hours — and the urine output tells you whether that number was right.
🧭 This page vs. its sibling — they are NOT the same page
NG-146 (this page) = the NUMBERS. Rule of 9's, the palm rule, Lund–Browder, pediatric proportions, the Parkland formula, the 8-hour/16-hour split, and worked practice problems.
NG-164 = the REHABILITATION PHASE. What happens after the wounds close: contracture prevention, positioning and splinting, pressure garments, water-based lotion, daily exercise, scar maturation, itch, sun protection, nutrition and psychosocial recovery.
Both come from the same source infographic, so they share a title — but do not study them as one page. This one is arithmetic; that one is recovery.
9️⃣ Everything is 9 or 18Head 9 · each arm 9 · front trunk 18 · back trunk 18 · each leg 18 · perineum 1 = 100%.
🧮 4 × kg × %TBSAParkland. Total Lactated Ringer's for the first 24 h from the time of injury.
⏳ Half in 8, half in 1650% of the total in the first 8 hours, the other 50% over the next 16 hours.
🚽 The number is a guessTitrate to urine ≥30 mL/hr, BP ≥90 systolic, HR <120. Never chase the formula instead of the patient.
📐
THE RULE OF NINES
STEP 1 · GET THE PERCENTAGE
Divide the adult body into chunks of 9% (plus one 1% chunk). Front and back are counted separately.
EXAM TIP Every region is split front/back. A whole arm is 9% — but only the front of that arm is 4.5%. That single habit fixes most Rule-of-Nines errors.
head & neckupper trunklower trunkarmslegsperineum 1%
🧠 “NINE ones: 9 head, 9+9 arms, 18+18 trunk, 18+18 legs, +1 for the perineum.” Add them: 9 + 18 + 36 + 36 + 1 = 100. If your total is not 100, you dropped a piece.
⭐ The three habits that stop Rule-of-Nines mistakes
↔️FRONT ≠ BACKalways ask which side
1️⃣ADD THE 1%perineum is easy to forget
🚫SKIP 1° BURNSsuperficial is not counted
🧍WHOLE LIMB?arm 9 · leg 18
➗HALF ITone surface = half the region
✅SUM CHECKcan't exceed 100
Only partial-thickness (2°) and full-thickness (3°/4°) burns are included in TBSA. A superficial (1°) sunburn is NOT counted — it does not leak the way deeper burns do, so counting it would over-estimate the fluid.
🧠 “First degree doesn't count.” If the stem says “reddened, painful, no blisters, blanches” — that region contributes 0%.
👶 Children are NOT small adults — the proportions change
Answer first: a child's head is proportionally much bigger and the legs proportionally smaller. Using the adult chart on an infant badly under-estimates the burn.
The most accurate method in children is the Lund–Browder chart, which assigns a different percentage to the head and legs for each age band. The pediatric Rule of Nines above is the quick bedside version.
🧠 “Babies are all head.” Head 18, each leg 13½ in the infant. As the child grows, the head loses ~1% per year and the legs gain it back.
🖐️
THE OTHER TWO METHODS
STEP 2 · WHEN 9's WON'T WORK
Rule of 9's is fast but blunt. Use the palm rule for scattered burns and Lund–Browder when accuracy matters.
🖐️ The palm (hand) rule — 1% per palm
Answer first: the patient's own palm including the fingers is roughly 1% of their TBSA. Use it for patchy, scattered or irregular burns that don't fill a whole 9% region.
🧠 “One hand, one percent.” Count palms for splash and spatter burns; count nines for whole-region burns.
🧾 Lund–Browder — the accurate one
A printed chart that assigns a percentage to each small body segment and adjusts the head/thigh/leg values by exact age band.
Most accurate method, and the standard in burn centers
Essential in children, where Rule of 9's is crudest
Slower — you shade a diagram and add up small numbers
Rule of 9's is the rapid field/ED estimate; Lund–Browder is the definitive one done later
🧠 “Nines for now, Lund–Browder for later.” Fast first, accurate second.
🚨 The classic errors — check yourself
Counting a whole leg (18%) when only the front was burned (9%)
Counting the 1° sunburn region into TBSA
Forgetting the perineum's 1% when the stem specifically mentions it
Using adult percentages on a toddler
Adding to more than 100%
Using the nurse's palm instead of the patient's
🧠 Read the stem twice: “anterior”, “posterior”, “entire”, “circumferential”. Those four words change the answer.
🧮
THE PARKLAND FORMULA
STEP 3 · TURN % INTO mL
Three numbers multiplied together. The hard part is not the multiplication — it is knowing what each number means.
🧮 4 mL × kg × %TBSA
The commonly taught version of the consensus (Parkland) formula for the first 24 hours after a major burn, given as Lactated Ringer's.
4 mL × body weight (kg) × %TBSA = total LR in the first 24 h→ ½ over the first 8 h · ½ over the next 16 h
🧠 “4 for the 4-alarm fire · half in 8.” Four milliliters, weight, burn percent — then cut it in half and put the first half in the first eight hours.
⏳ The clock starts at the TIME OF INJURY — not arrival
This is the highest-yield trap in the whole topic. If a patient is burned at 08:00 and reaches you at 10:00, you have 6 hours left to deliver the first half — so the rate has to be higher, not the same.
🧠 “The burn started the stopwatch, not the ambulance.” Always ask what time did this happen?
➗ Turning the total into an hourly rate
Exam questions often want the mL/hr, not just the total. Two divisions:
first 8 h rate = (total ÷ 2) ÷ 8next 16 h rate = (total ÷ 2) ÷ 16
The first-8-hour rate is always double the next-16-hour rate
If hours have already been lost, divide by the hours remaining in that block
Weight in pounds? ÷ 2.2 to get kilograms first
🧠 “Front-load it.” The leak is worst early, so the fluid goes in fastest early.
💧 After the first 24 hours
The capillary leak begins to seal, so the plan changes.
Crystalloid volume is reduced and titrated down as urine output allows
Colloid (e.g. albumin) is often added in the second 24 hours in many protocols, once capillaries are less leaky, to hold fluid in the vessels
Maintenance fluid (often with dextrose) replaces evaporative loss
Electrolytes flip: potassium falls, H&H falls with hemodilution — see NG-107
Watch hard for the swing to fluid overload during diuresis: crackles, JVD, dyspnea, sudden weight gain
🧠 “Day 1 fill the tank · Day 2 seal the tank.”
🎯
WORKED PRACTICE
STEP 4 · DO THE MATH
Cover the answer, work it on paper, then check. Three of these are lifted straight from the classic question banks.
🎓 Example 1 — full-thickness burns to ALL posterior surfaces
A client has full-thickness burns to all posterior body surfaces. Using the Rule of 9's, calculate the % TBSA affected.
back of head & neck …… 4.5%entire back (upper 9 + lower 9) …… 18%back of both arms (4.5 × 2) …… 9%back of both legs (9 × 2) …… 18%4.5 + 18 + 9 + 18 = 49.5% TBSA
Why students miss it: they use whole-limb values (9% per arm, 18% per leg) instead of halving for the posterior surface only.
🧠 “All the back = just under half the body.”49.5% — remember it as “about 50%.”
🎓 Example 2 — anterior legs + perineum
A client has partial-thickness burns to the anterior legs and the perineum. Calculate the % TBSA.
front of right leg …… 9%front of left leg …… 9%perineum …… 1%9 + 9 + 1 = 19% TBSA
Why students miss it: they forget the perineum's 1% and answer 18%, or they count whole legs and answer 37%.
🧠 “18 + the little 1.” When the stem says perineum, it is because that 1% is the point of the question.
🎓 Example 3 — now turn it into milliliters
The client above weighs 100 kg with 19% TBSA. Calculate the Lactated Ringer's fluid resuscitation needed.
4 mL × 100 kg × 19 %TBSA= 7,600 mL in the first 24 hours½ = 3,800 mL in the first 8 hours → 475 mL/hr½ = 3,800 mL over the next 16 hours → 237.5 mL/hr
🧠 “Same halves, different speeds.” Equal volumes, but the first one has to go in twice as fast.
🎯 Your turn — three to try
Practice A · 70 kg adult, burns to the entire front of the trunk and the whole right arm
TBSA?
Anterior trunk 18% + whole right arm 9% = 27% TBSA.
Parkland total and first-8-hour rate?
4 × 70 × 27 = 7,560 mL in 24 h. Half = 3,780 mL in the first 8 h → 472.5 mL/hr; then 3,780 mL over 16 h → 236.25 mL/hr.
Practice B · 80 kg adult, burns to the head and neck (all round), anterior trunk, and both anterior legs
TBSA?
Head and neck all round 9% + anterior trunk 18% + anterior legs 9 + 9 = 45% TBSA.
Parkland total?
4 × 80 × 45 = 14,400 mL in 24 h. First 8 h: 7,200 mL → 900 mL/hr. Next 16 h: 7,200 mL → 450 mL/hr. (A burn this size also needs an airway assessment first — head and neck burns.)
Practice C · 154 lb adult, posterior trunk and the back of both legs, burned 3 hours before arrival
Weight in kg and TBSA?
154 ÷ 2.2 = 70 kg. Posterior trunk 18% + posterior legs 9 + 9 = 36% TBSA.
Total, and the rate for the remainder of the first 8-hour block?
4 × 70 × 36 = 10,080 mL total. Half = 5,040 mL must be in by 8 hours after the injury. Three hours are already gone, so it has to run over the remaining 5 hours → 5,040 ÷ 5 = 1,008 mL/hr. Then 5,040 mL over the next 16 h → 315 mL/hr. Titrate to urine output throughout.
🧠 Do these on paper, out loud, three days in a row. Burn math is the cheapest set of marks in the whole integumentary unit.
⚡
QUICK RECALL
SAY IT OUT LOUD
9 · 9 · 18 · 18 · 18 · 1Head · each arm · front trunk · back trunk · each leg · perineum = 100%.
🖐️ 1 palm = 1%Patient's palm + fingers. Use it for scattered burns.
🧮 4 × kg × %Parkland total of LR for 24 h. Half in 8 h, half in 16 h, clock from injury.
🚽 Urine rules the rate≥30 mL/hr, BP ≥90, HR <120. The formula only starts the infusion.
🎯 Cover & check — 7 rapid-fire questions
Q1: What percentage is the anterior trunk in an adult?
18% — chest 9% plus abdomen 9%. The posterior trunk is another 18%.
Q2: A whole arm, all the way round? A whole leg?
Arm = 9% (4.5% front + 4.5% back). Leg = 18% (9% front + 9% back).
Q3: Is a first-degree sunburn counted in TBSA?
No. Only partial-thickness and full-thickness burns are counted. Including superficial burns would overestimate the fluid requirement.
Q4: What are the infant modifications?
Head 18% (instead of 9%) and each leg about 13.5% (instead of 18%). Arms and trunk are unchanged. The Lund–Browder chart is the accurate age-adjusted method.
Q5: State the Parkland formula and the split.
4 mL × body weight in kg × %TBSA = total Lactated Ringer's for the first 24 hours. Half in the first 8 hours, the remaining half over the next 16 hours, timed from the moment of injury.
Q6: A 60 kg client with 30% TBSA — total volume and first-8-hour rate?
4 × 60 × 30 = 7,200 mL total. Half = 3,600 mL in the first 8 hours = 450 mL/hr. Then 3,600 mL over 16 hours = 225 mL/hr.
Q7: The calculated rate is running but urine output is 15 mL/hr. What now?
The patient is under-resuscitated. Report it and anticipate an order to increase the Lactated Ringer's. The formula is only an estimate — urine output, blood pressure and heart rate steer the actual rate.
📚 Where to go next
NG-164 — Rehabilitation phase — this page's sibling: what happens after the wounds close. Positioning, pressure garments, lotion, daily exercise, scars and psychosocial recovery.