What is Paediatric Weight Estimation (Broselow)?
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The APLS (Advanced Paediatric Life Support) weight estimation formula is a rapid bedside tool used by emergency clinicians to estimate a child's weight in kilograms when it cannot be measured directly. In emergencies, weight is critical because virtually all drug doses, fluid boluses, and equipment sizes are weight-based in paediatrics. The primary APLS formula — Weight (kg) = 2 × (age in years + 4) — applies to children aged 1 to 10 years. For infants under 1 year, a different approximation is used: approximately 0.5 kg per month up to 6 months, then slower gain. The Best Guess formula, Weight (kg) = 3 × age + 7, tends to perform better for older children (over 5 years) and in populations where children are larger than historical UK norms. The Broselow tape is a colour-coded length-based tool providing weight estimation alongside pre-calculated drug doses and equipment sizes for each colour zone, widely regarded as the gold standard when a tape can be applied. Length-based estimation consistently outperforms age-based formulae because weight gain varies more by height than age. Despite its limitations, the APLS formula remains embedded in resuscitation training worldwide because it requires no equipment, is fast to apply, and provides a clinically safe starting point. All emergency drug doses — adrenaline, atropine, glucose, lorazepam, crystalloid boluses — are calculated from this estimated weight, making accuracy vital to patient safety.
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Formula
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APLS Weight (kg) = 2 × (age_years + 4) [for age 1-10yr]; Best Guess = 3 × age_years + 7; Infant (<1yr) ≈ 0.5 kg/month (up to 6mo) then ~0.25 kg/month; Broselow tape: length-based colour zone lookupVariable Legend
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| Symbol | Name | Unit | Description |
|---|---|---|---|
| W | Estimated Weight | kg | Derived from age or length; used for all drug and fluid calculations |
| A | Age | years | Age in whole years; primary input for APLS and Best Guess formulae |
| BW | Birth Weight | kg | Used for infant weight estimation alongside postnatal age in months |
How to Paediatric Weight Estimation (Broselow)
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- 1Determine the child's age in whole years from history or documentation; if unknown, use the Broselow tape measured from crown to heel.
- 2For children aged 1-10 years apply the APLS formula: add 4 to the age in years, then multiply by 2 to obtain estimated weight in kilograms.
- 3For children older than 5 years, or in populations known to be larger, consider the Best Guess formula (3 × age + 7) as it tends to give higher and more accurate estimates for older children.
- 4For neonates and infants under 1 year, use birth weight plus incremental gain: approximately 0.5 kg/month for the first 6 months, slowing thereafter; a term neonate weighs approximately 3.5 kg.
- 5If a Broselow tape is available, lay it alongside the supine child from the top of the head to the heel and read the colour zone — each zone provides pre-calculated drug doses and equipment sizes without needing weight.
- 6Record the estimated weight clearly in the resuscitation documentation and use it consistently for all drug and fluid calculations throughout the resuscitation.
- 7Verify against actual weight as soon as a scale is available and recalculate doses if the discrepancy is clinically significant (>20% difference).
Worked Examples
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Adrenaline 0.1 mL/kg of 1:10,000 = 1.4 mL; fluid bolus 10 mL/kg = 140 mL NS
APLS formula gives 14 kg for a 3-year-old. Drug doses and fluid boluses are then derived directly from this weight, making a rapid and reliable estimate essential.
Best Guess typically more accurate for school-age children; use 28 kg
The 6 kg difference between the two formulae is clinically significant. For older children, the Best Guess formula has been shown to correlate more closely with actual weights in modern populations.
Resuscitation adrenaline = 0.1 mL/kg 1:10,000 = 0.54 mL
Infants gain approximately 0.5 kg per month in the first 6 months. Knowing birth weight improves accuracy significantly compared to using a generic formula.
Tape provides adrenaline, atropine, glucose, lorazepam, and equipment sizes directly
The Broselow tape removes the calculation step entirely by providing colour-coded, pre-calculated doses at the bedside, reducing cognitive load during resuscitation.
Real-World Applications
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Emergency drug dose calculation for adrenaline, atropine, glucose, lorazepam, and other resuscitation drugs in paediatric cardiac arrest., representing an important application area for the Pals Weight in professional and analytical contexts where accurate pals weight calculations directly support informed decision-making, strategic planning, and performance optimization
Fluid resuscitation volume calculation — 10-20 mL/kg NS boluses in septic shock or trauma., representing an important application area for the Pals Weight in professional and analytical contexts where accurate pals weight calculations directly support informed decision-making, strategic planning, and performance optimization
Equipment size selection — endotracheal tube size (age/4 + 4), blade size, and laryngeal mask size all derive from weight or age., representing an important application area for the Pals Weight in professional and analytical contexts where accurate pals weight calculations directly support informed decision-making, strategic planning, and performance optimization
Calculating defibrillation energy — 4 J/kg for paediatric VF/pVT, updated after each shock., representing an important application area for the Pals Weight in professional and analytical contexts where accurate pals weight calculations directly support informed decision-making, strategic planning, and performance optimization
Teaching and simulation: APLS and PALS courses worldwide use weight estimation as a core curriculum component to prepare trainees for real emergencies., representing an important application area for the Pals Weight in professional and analytical contexts where accurate pals weight calculations directly support informed decision-making, strategic planning, and performance optimization
Special Cases
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Premature Neonates
In the Pals Weight, this scenario requires additional caution when interpreting pals weight results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when pals weight calculations fall into non-standard territory.
Obese Children
In the Pals Weight, this scenario requires additional caution when interpreting pals weight results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when pals weight calculations fall into non-standard territory.
Children with Chronic Illness or Malnutrition
In the Pals Weight, this scenario requires additional caution when interpreting pals weight results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when pals weight calculations fall into non-standard territory.
Cardiac Arrest in the Older Child
{'title': 'Cardiac Arrest in the Older Child', 'body': 'In children over 12-14 years approaching adult size, adrenaline and defibrillation energy may reach adult ceilings. Adrenaline maximum is 1 mg regardless of weight; defibrillation maximum with standard paediatric calculation (4 J/kg) should be capped at adult energies (360 J monophasic or 200 J biphasic) if estimated weight exceeds 50 kg.'}
APLS Weight Estimates by Age
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| Age | APLS Formula (kg) | Best Guess (kg) | Typical Broselow Zone |
|---|---|---|---|
| 1 year | 10 | 10 | Pink |
| 2 years | 12 | 13 | Red |
| 3 years | 14 | 16 | Purple |
| 5 years | 18 | 22 | Yellow |
| 7 years | 22 | 28 | White |
| 10 years | 28 | 37 | Blue/Orange |
Frequently Asked Questions
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What is the APLS weight estimation formula?
The APLS weight estimation formula is a tool used to estimate a child's weight in kilograms, calculated as (age in years x 2) + 4 for children aged 1-12 years. For example, a 5-year-old child would have an estimated weight of (5 x 2) + 4 = 14 kilograms. This formula provides a quick and reliable method for estimating a child's weight when it cannot be measured directly.
How is the APLS weight estimation used in emergency situations?
In emergency situations, the APLS weight estimation is used to calculate drug doses, fluid boluses, and equipment sizes. For instance, if a child needs a dose of epinephrine, the estimated weight would be used to calculate the correct dosage, typically 10-20 micrograms per kilogram. Accurate weight estimation is critical to ensure the child receives the correct treatment.
What are the typical weight ranges for children using the APLS formula?
Using the APLS formula, the estimated weights for children range from approximately 6 kilograms for a 1-year-old to 36 kilograms for a 12-year-old. For example, a 2-year-old child would have an estimated weight of (2 x 2) + 4 = 8 kilograms, while a 10-year-old child would have an estimated weight of (10 x 2) + 4 = 24 kilograms.
What are common mistakes to avoid when using the APLS weight estimation formula?
One common mistake to avoid is using the formula for children outside the recommended age range of 1-12 years. Another mistake is not rounding the estimated weight to the nearest whole number, as this can lead to inaccurate calculations. Additionally, it is essential to remember that the APLS formula is an estimation and may not reflect the child's actual weight.
Can you provide a real-world example of using the APLS weight estimation in an emergency?
For example, in a situation where a 4-year-old child is experiencing cardiac arrest, the APLS weight estimation formula would be used to estimate the child's weight as (4 x 2) + 4 = 12 kilograms. This estimated weight would then be used to calculate the correct dose of epinephrine, such as 1 milligram (10 micrograms per kilogram x 12 kilograms) per dose, and to determine the correct size of equipment, such as a pediatric advanced airway device.
Common Mistakes to Avoid
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- !Using the APLS formula for children over 10 years, which significantly underestimates weight and leads to underdosing.
- !Forgetting to apply maximum dose ceilings — for example, adrenaline max 1 mg and atropine max 0.6 mg regardless of calculated dose.
- !Confusing age in months with age in years when applying the formula for infants, leading to grossly incorrect estimates.
- !Measuring Broselow tape from the wrong end (feet rather than head) or with the child flexed rather than supine.
- !Using the same weight estimate for an obese child as for a normal-weight child of the same age, resulting in drug overdose.
- !Failing to document the estimated weight used, making it impossible to verify dose calculations during resuscitation review.
Pro Tip
In a paediatric resuscitation, calculate and display the weight estimate prominently at the bedside. Pre-calculate the top five drug doses (adrenaline, atropine, glucose, lorazepam, fluid bolus) from this weight before they are needed — this reduces cognitive load and errors at the critical moment.
Did you know?
The Broselow tape was developed by Dr James Broselow in the early 1980s after he observed that resuscitation teams were struggling to calculate paediatric drug doses under stress. He noticed that weight correlates better with length than age, a simple insight that has since saved countless lives by converting a complex calculation into a colour lookup.
References
- ›Advanced Paediatric Life Support (APLS) 6th Edition — BMJ Books / Wiley
- ›Luscombe MD, Owens BD. Weight estimation in resuscitation: is the current formula still valid? Arch Dis Child 2007.
- ›Broselow J et al. A length-based method for estimating paediatric weight and medication dosing. Ann Emerg Med 1988.
- ›Resuscitation Council UK — Paediatric Advanced Life Support Guidelines 2021
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