How do I dose defibrillation energy in a child if I only have an estimated weight?

Defibrillation energy for pediatric VF/pulseless VT: 4 J/kg initial dose, repeat at 4 J/kg or increase to 6–10 J/kg for subsequent shocks (maximum 200 J). For a child with estimated weight of 20 kg: initial shock = 80 J (4 × 20). Estimated weight introduces a degree of uncertainty in defibrillation dosing, but within the range of reasonable weight estimation accuracy (±20%), defibrillation doses are not as weight-sensitive as drug doses — under- or overdosing by 20% is clinically acceptable. Use the APLS-estimated or Broselow weight for defibrillation and proceed without delay; CPR quality and early defibrillation are more important than exact energy calculation.

At what age do APLS formulas stop being useful?

APLS formulas are designed for children ages 1–14 years. For adolescents >14 years, adult dosing may be appropriate if the patient's size is adult-equivalent. Evaluate whether the adolescent has adult body habitus (>50 kg) and use clinical judgment. The Broselow tape covers up to ~36 kg (~12 years). For adolescents over these ranges, standard adult weight-based dosing applies. For infants <1 month (neonates), APLS is unreliable — use actual measured weight from the medical record or nursery chart.

What should I do if the parents report a weight very different from the APLS estimate?

Trust the parents. Parent-reported weight is typically within 5–10% of actual weight and is more accurate than formula-based estimates. If parents report a weight significantly different from the APLS formula (e.g., parents say 'he's 30 kg' but APLS estimates 20 kg for his age), use the parent-reported weight for drug dosing. Document both values: 'Parent-reported weight 30 kg; APLS estimate for age 8 = 31 kg — concordant. Drug doses calculated on 30 kg.' If parent-reported and formula weights diverge significantly, note the discrepancy and use clinical judgment or obtain actual weight.

Why is APLS weight estimation important in pediatric emergency medicine?

Virtually all pediatric emergency drugs, IV fluids, defibrillation energy, and equipment sizes are weight-based. Without weight, safe dosing is impossible. In emergencies, weighing a child is often not feasible — the child may be in cardiac arrest, actively seizing, in respiratory failure, or combative. Weight estimation (using APLS, Broselow tape, or parent report) provides the critical weight needed for immediate, safe drug dosing. Studies show that providers who use systematic weight estimation tools make significantly fewer dosing errors than those who guess weight without structured tools.

Can APLS weight formulas be used for fluid resuscitation dosing?

Yes. APLS-estimated weight can be used for initial fluid bolus calculations in septic shock or dehydration emergencies. Standard fluid bolus: 10–20 mL/kg of isotonic crystalloid (0.9% NaCl or Ringer's lactate) IV or IO over 5–20 minutes. For septic shock: start with 10 mL/kg and reassess to avoid fluid overload. Maintenance IV fluids (Holliday-Segar method): 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr for each kg above 20 kg. As with all weight-dependent calculations, transition to actual measured weight for ongoing fluid management as soon as possible.

What are the most dangerous dosing errors in pediatric emergency medicine?

The most common and dangerous pediatric drug dosing errors in emergency medicine include: (1) 10-fold epinephrine overdose — giving 0.1 mg/kg instead of 0.01 mg/kg for cardiac arrest or anaphylaxis. (2) Weight-based errors — using adult dosing for children or failing to adjust for actual vs estimated weight. (3) Concentration errors — using 1:1,000 instead of 1:10,000 epinephrine for IV administration. (4) Underdosing anticonvulsants — leading to treatment failure in status epilepticus. (5) Overdosing sedatives/opioids based on overestimated weight. Independent double-checking of all high-alert pediatric medications before administration is the most effective error-prevention strategy.

Online Medical Tools — Pediatric Weight Estimate

Printed on 6/30/2026

For informational purposes only. This is not medical advice.

Pediatrics

Pediatric Weight Estimate

The APLS (Advanced Paediatric Life Support) weight estimation calculator provides a quick weight estimate for children based on age. This is critical in pediatric emergencies when a measured weight is unavailable and time-sensitive medication dosing, fluid resuscitation, or equipment sizing is needed. The formulas vary by age group: infants use (age_months × 0.5) + 4, children 1–5 use (age × 2) + 8, and children 6–14 use (age × 3) + 7. While always an approximation, these estimates provide a reasonable starting point until an actual weight can be obtained. Use the estimated weight in [Pediatric Dose Calculator](/tools/pediatric-dose) for weight-based drug dosing. In pediatric emergencies, assess consciousness with [Pediatric GCS](/tools/pediatric-gcs) and [Glasgow Coma Scale](/tools/glasgow-coma-scale). Monitor the critically ill child with [SOFA Score](/tools/sofa-score) and [APACHE II](/tools/apache-ii).

Formula: Age 1–5: (2 × age) + 8 kg. Age 6–14: (3 × age) + 7 kg.

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How It Works

Determine the child's age and select the appropriate APLS formula

The APLS weight estimation formula uses age as the sole variable. Determine the child's age in years (round to the nearest year for children ≥1 year; use months for infants <1 year). Apply the correct formula for the age group: Infants <1 year: Weight (kg) = (age in months × 0.5) + 4. This gives estimates ranging from ~4 kg at birth to ~10 kg at 12 months. Children 1–5 years: Weight (kg) = (age × 2) + 8. This gives estimates from 10 kg at age 1 to 18 kg at age 5. Children 6–14 years: Weight (kg) = (age × 3) + 7. This gives estimates from 25 kg at age 6 to 49 kg at age 14. For children >14 years, adult dosing may be appropriate depending on size. Note: This calculator uses the updated APLS formulas (not the classic 2×(age+4) formula for all ages), which improve accuracy across age groups.

Use the estimated weight to calculate emergency drug doses and select equipment sizes

Once the estimated weight is obtained, apply it systematically for time-critical emergency calculations: Drug dosing: Epinephrine 1:10,000 IV for cardiac arrest: 0.01 mg/kg (0.1 mL/kg). Epinephrine 1:1,000 IM for anaphylaxis: 0.01 mg/kg (max 0.5 mg). Atropine: 0.02 mg/kg (min 0.1 mg). Adenosine: 0.1 mg/kg (max 6 mg, first dose). Fluid bolus for septic shock: 10–20 mL/kg IV over 5–20 minutes. Glucose for hypoglycemia: 2 mL/kg of 10% dextrose. Defibrillation: 4 J/kg (initial), up to 8–10 J/kg (subsequent). Equipment sizing: ETT size (uncuffed): (age/4) + 4; (cuffed): (age/4) + 3.5. Laryngoscope blade: Miller 1 (<2 yr), Miller 2 or Macintosh 2 (2–5 yr). Always cross-check calculated doses with the Broselow tape or a pre-printed pediatric emergency drug card. The second provider should independently verify all high-risk drug doses before administration.

Transition to measured weight as soon as clinically possible

Weight estimation is a bridge, not a substitute. Once the child is stabilized and a scale is accessible (ED bed scale, calibrated infant scale), obtain actual weight and recalculate all ongoing drug infusions and doses based on measured weight. This is particularly important for: continuous infusions (dopamine, epinephrine infusions in mg/kg/min), repeat doses of high-risk medications (opioids, benzodiazepines, neuromuscular blockers), maintenance IV fluid calculation (Holliday-Segar method: 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr for each kg above 20 kg). Document the estimated weight used for initial emergency doses and the actual weight when measured. If the estimated weight significantly overestimated actual weight (e.g., malnourished child), reassess for potential drug overdosing and monitor clinical response closely.

Who Uses the Pediatric Weight Estimate

Pediatric Cardiac Arrest and Resuscitation

Emergency physicians, PICU intensivists, and pediatric code teams

In pediatric cardiac arrest, weight estimation enables immediate calculation of resuscitation drug doses and defibrillation energy without delaying CPR. APLS formula provides rapid weight estimate when a scale is not accessible during active resuscitation. Critical doses that require weight: epinephrine 0.01 mg/kg IV/IO (most weight-sensitive medication — errors can be fatal), amiodarone 5 mg/kg IV/IO for VF/pulseless VT, adenosine 0.1 mg/kg (SVT), defibrillation 4 J/kg. Pre-code weight estimation by family (parents often know their child's weight) or Broselow tape should be attempted before using APLS formula. Cross-check APLS estimate with Broselow tape or pediatric code dosing sheet for all resuscitation drugs.

Rapid Sequence Intubation (RSI) Drug Dosing

Emergency physicians and anesthesiologists managing pediatric airways

RSI in children requires weight-based dosing of premedication, induction agent, and neuromuscular blocker. When actual weight is unavailable, APLS estimate enables timely preparation of RSI medications. Standard RSI regimen (ages vary): atropine 0.02 mg/kg IV (min 0.1 mg, max 0.5 mg) — pretreatment in children <1 yr. Ketamine 1.5–2 mg/kg IV or etomidate 0.3 mg/kg IV (induction). Succinylcholine 1–2 mg/kg IV (pediatric <10 kg: 2 mg/kg; >10 kg: 1.5 mg/kg) or rocuronium 1.2 mg/kg IV. Prepare drugs by weight before patient arrival for anticipated pediatric airways (trauma, anaphylaxis, status epilepticus). APLS-estimated weight allows this preparation while the team simultaneously attempts to obtain measured weight.

Pre-Hospital Pediatric Emergency Care

Paramedics and emergency medical technicians

Pre-hospital providers often encounter critically ill or injured children without access to a scale. APLS weight formula enables paramedics to calculate drug doses and select equipment (ETT size, defibrillation pads, IV catheter size) during transport. Pre-printed weight-based drug calculation cards are standard in pediatric emergency kits and often use APLS-estimated weights for age-based dosing guides. Many EMS systems use Broselow tape as the primary weight estimation tool — APLS formula serves as a backup when the tape is unavailable or the child is beyond the tape's weight range. Communicate estimated weight to the receiving hospital during radio or phone report for medication preparation.

Status Epilepticus Management

Pediatric neurologists and emergency physicians

Status epilepticus treatment in children requires weight-based anticonvulsant dosing. Standard protocol: lorazepam 0.1 mg/kg IV (max 4 mg) or diazepam 0.5 mg/kg PR (max 20 mg) for first-line benzodiazepine. Levetiracetam 20–60 mg/kg IV over 15 min (max 3000 mg) or fosphenytoin 20 mg PE/kg IV for second-line. Phenobarbital 20 mg/kg IV for refractory status. Midazolam continuous infusion for super-refractory status: 0.05–0.4 mg/kg/hr. Accurate weight-based dosing is critical because underdosing anticonvulsants is a major cause of treatment failure in pediatric status epilepticus. When actual weight is unavailable, APLS estimate ensures appropriate (rather than fixed adult-equivalent) dosing.

Anaphylaxis Management with Epinephrine Dosing

All pediatric emergency providers

Epinephrine is the most important drug in anaphylaxis, and weight-based dosing is critical — underdosing is potentially fatal, overdosing causes severe hypertension and arrhythmia. Standard dosing: epinephrine 1:1,000 IM (anterolateral thigh): 0.01 mg/kg, max 0.5 mg per dose. Pre-loaded auto-injectors are sized for <15 kg (0.1 mg), 15–30 kg (0.15 mg), and >30 kg (0.3 mg). APLS weight estimate guides manual epinephrine dosing when auto-injectors are unavailable or the child's weight is outside auto-injector ranges. Second dose if no response: same dose after 5–15 minutes. Parents often know their child's weight for emergency reference — always ask before using estimated weight for epinephrine.

Pro Tips

Always ASK parents for their child's weight before using APLS estimate

The single most accurate 'tool' for pediatric weight estimation in a crash cart scenario is the parents themselves. Before using any formula, ask: 'Do you know how much your child weighs? Did they have a recent checkup?' Many parents know their child's exact weight from the last well-child visit. Parent-reported weight is typically within 5–10% of actual weight and is more accurate than formula-based or tape-based estimates. If parents are unsure, ask: 'About how heavy is your child — closer to 15 kg (like a 2-year-old) or 25 kg (like a 7-year-old)?' This rough estimate still provides better guidance than formula alone.

Broselow tape is preferred over APLS formula when available — use both as cross-checks

The Broselow-Luten tape is a length-based weight estimation tool validated as more accurate than age-based formulas for most individual children. When a Broselow tape is available, it is the preferred single tool for weight estimation. APLS formula and Broselow tape serve as cross-checks: if both give similar estimates (within ~10–15%), proceed with confidence. If they diverge significantly, the child may be unusually tall/short for age or obese — use clinical judgment and try to obtain actual weight. Most pediatric emergency programs stock Broselow tapes as standard equipment. APLS formula is the backup when the tape is unavailable or the child is outside its weight range (>36 kg).

APLS underestimates weight in obese children — upward adjustment may be needed

Childhood obesity rates have increased dramatically since APLS formulas were derived, particularly in Western countries. Studies from the US, UK, and Australia consistently show APLS formulas underestimate actual weight by 15–25% in current pediatric populations. This means drug doses based on APLS estimates may be underdosed. For children who visually appear obese or larger than typical for their age, consider upward adjustment of the estimated weight. However, for obese children, some drugs (particularly lipophilic drugs like phenytoin, digoxin) should be dosed based on ideal body weight, not actual weight — use clinical judgment for each drug class.

For neonates and premature infants, do not use APLS — use actual weight

APLS formulas are not validated for neonates (first 28 days of life) or premature infants. Neonatal weight varies enormously based on gestational age (23-week premature infant ~600 g; 40-week term infant ~3500 g) and cannot be reliably estimated from age alone. For all NICU and nursery patients, actual measured weight is mandatory before drug dosing. Even in emergency situations in the NICU, a reliable weight should be readily available from the medical record or on the isolette/warmer. The only acceptable APLS formula for infants ≥1 month is the infant formula: (age in months × 0.5) + 4, which gives reasonable estimates for well-grown infants.

Double-check high-alert medications — never give based on estimate alone

For high-alert pediatric medications where weight errors can cause severe harm, a second independent verification is standard of care regardless of whether actual or estimated weight is used. High-alert medications requiring independent double-check: epinephrine (cardiac arrest, anaphylaxis), insulin, opioids (morphine, fentanyl, hydromorphone), concentrated electrolytes (KCl, hypertonic saline), neuromuscular blockers, and vasoactive infusions (dopamine, norepinephrine). The 10-fold epinephrine dosing error (giving 0.1 mg/kg instead of 0.01 mg/kg) is one of the most dangerous pediatric medication errors — always confirm the dose independently before administration.

Use pre-printed Broselow-based resuscitation drug cards in emergency settings

Many hospitals and emergency departments use pre-printed resuscitation drug calculation cards or tablets organized by patient weight (Broselow zones) that list common emergency drug doses for that weight range. These cards eliminate calculation errors during high-stress emergencies. If your institution has such a system, use it in conjunction with APLS weight estimation — look up the appropriate weight-based column on the pre-printed card rather than calculating each dose individually during a resuscitation. Emergency Nursing Pediatric Course (ENPC) and PALS courses teach standardized approaches to these tools. Verify your institution has an up-to-date version of these reference cards.

Luscombe-Owens formula is a useful alternative for older children

The Luscombe and Owens formula (Emerg Med J, 2007) is: Weight = 3 × age + 7 for children 1–12 years. This formula was derived from a UK population and may provide better accuracy than the classic APLS formula for school-age children in well-nourished Western populations. It is simple and widely used as an alternative. The Traub-Johnson formula (2.396 × e^(0.01863 × height in cm)) is even more accurate when height is available but requires a calculator. When multiple formulas are available, use the method that best fits the clinical context — age-based for rapid estimates, height-based when time and a measuring tape are available.

Common Questions About Your Results

You are correct to be concerned — APLS formulas systematically underestimate weight in obese children. For a visually obese child, the true weight may be 25–50% above the APLS estimate. If any means of actual weighing is available (even an approximate bed scale in the ED), use it. If not, estimate the degree of obesity visually and consider adjusting the estimated weight upward. For most drugs in an acute emergency (resuscitation, RSI, anticonvulsants), dosing based on slightly underestimated weight is safer than overdosing. However, insulin, some anticonvulsants, and certain chemotherapy drugs should be dosed on ideal body weight even for obese children — consult a pharmacist or reference for obesity-specific pediatric dosing guidance.

If APLS formula and Broselow tape diverge significantly (>15–20%), the child is likely either unusually tall or short for age, obese, or malnourished. The Broselow tape is generally more accurate because it is based on the child's actual length (a better proxy for lean body mass than age). However, Broselow tape loses accuracy for children weighing >36 kg (outside the tape's calibrated range). For a child who appears large for age, trust the higher estimate (use clinical judgment). If possible, obtain actual weight — even an approximate scale reading is better than relying on either formula when they disagree significantly.

Rapid weight estimation in cardiac arrest: (1) Ask the bystander/parent immediately — most know their child's weight. (2) Apply Broselow tape if available (measure length, read weight from color zone). (3) If neither is available, estimate age from appearance and apply APLS formula. (4) If age is unknown, estimate age from physical development: infant (<1 year), toddler (1–3 years), preschool (3–5 years), school-age (6–12 years), adolescent (12+ years). Most hospital resuscitation carts have Broselow tapes attached. Initiate CPR and ventilation immediately while weight estimation occurs in parallel — do not delay starting resuscitation to calculate exact drug doses.

No. Estimated weight should be used only for initial emergency doses. Once the patient is stabilized and a scale is accessible, obtain actual measured weight and recalculate all ongoing infusions. Continuous infusions (vasoactive drugs, opioid infusions, propofol) are weight-based and run over extended periods — errors compound over time. A continuous epinephrine infusion calculated on a 20% overestimated weight would deliver 20% too much drug every hour. Transition to measured weight as soon as possible after any pediatric emergency, document both weights in the chart, and explicitly note when medication doses were recalculated based on actual weight.

Evidence-Based Methodology

APLS weight formula (2×(age+4) for 1–4yr and 3×age for 5–14yr) was derived from the Advanced Paediatric Life Support course. Luscombe & Owens (Emerg Med J 2007) found it underestimates weight in a UK population by ~20%. Traub & Johnson formula (2.396 × e^0.01863×height in cm) is more accurate when height is available. PALS 2020 guidelines and ERC guidelines recommend actual weight or Broselow tape as preferred over age-based formulas.

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

The estimated weight provides an approximate body weight in kilograms based on the child's age using the APLS formulas. For infants under 1 year, the formula (age in months x 0.5) + 4 gives typical weights ranging from 4 kg at birth to 10 kg at 12 months. For children aged 1-5, the formula (age x 2) + 8 gives estimates from 10 kg to 18 kg. For children 6-14, the formula (age x 3) + 7 yields estimates from 25 kg to 49 kg.

This estimate should be used as an immediate starting point for emergency calculations such as medication dosing (e.g., epinephrine, amiodarone), defibrillation energy levels, fluid bolus volumes, and equipment sizing (endotracheal tube, laryngoscope blade). For resuscitation medications, the estimated weight provides a dose that is safe to administer while awaiting a measured weight. Once the patient is stabilized, always transition to a measured weight for ongoing management.

It is important to remember that this is a population average. Individual children may vary significantly from the estimate based on their nutritional status, genetics, and growth trajectory. The actual weight of any given child may differ from the APLS estimate by 20% or more.

When to Use This Tool

Use this calculator in pediatric emergency situations when a measured weight is not immediately available and time-critical interventions cannot be delayed. The most common scenarios include cardiac arrest, anaphylaxis, status epilepticus, rapid sequence intubation, and severe sepsis requiring urgent fluid resuscitation. In these situations, even an approximate weight is far better than no weight at all, as virtually all pediatric medications and interventions are weight-based.

The APLS formulas are also useful for pre-hospital providers who need to prepare medications and equipment during transport. Knowing the estimated weight before arrival allows EMS teams to have the correct drug doses drawn up and the appropriate equipment sizes ready. The formulas can serve as a cross-check for length-based estimates (e.g., Broselow tape) to flag potential discrepancies.

Limitations

APLS weight formulas are population-based estimates derived from historical growth data and tend to underestimate weight in well-nourished Western populations where childhood obesity rates have increased significantly since the formulas were developed. Studies in countries like the United States, United Kingdom, and Australia have found that APLS estimates underestimate actual weight by 10-20% in many children, particularly those over age 5.

Conversely, in malnourished populations or developing countries, APLS formulas may overestimate weight. This is clinically important because overestimation could lead to medication overdosing. In any population where malnutrition or obesity is prevalent, the formula should be used with particular caution.

Length-based methods such as the Broselow tape are generally considered more accurate than age-based formulas for individual weight estimation because they account for the child's actual size rather than age alone. When available, the Broselow tape should be preferred. Additionally, these formulas do not apply to premature infants or neonates in the first month of life, who require gestational age-based weight estimates. For children with chronic conditions affecting growth (e.g., cerebral palsy, Down syndrome, growth hormone deficiency), standard age-based formulas will be particularly inaccurate.

For related assessments, see Pediatric Dose and Pediatric GCS.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.

Changelog

April 21, 2026 · trust-baseline
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Frequently Asked Questions

The Advanced Paediatric Life Support (APLS) weight formulas are: Infants (<1 year): Weight (kg) = (age in months × 0.5) + 4. Children 1–5 years: Weight (kg) = (2 × age) + 8. Children 6–14 years: Weight (kg) = (3 × age) + 7. These formulas provide approximate weight estimates for emergency situations when actual weight cannot be measured. They are the standard weight estimation method taught in pediatric emergency courses including APLS, PALS, and ENPC.

APLS formulas are moderately accurate but systematically underestimate weight in current Western pediatric populations due to increasing childhood obesity rates. Studies from the US, UK, and Australia show APLS formulas underestimate actual weight by 10–20% in many children, particularly those over age 5. The Broselow tape (length-based) is generally more accurate for individual children and is the preferred tool when available. For most emergency drug dosing, APLS estimates are close enough to be safe, but actual weight should be obtained as soon as clinically feasible.

Use weight estimation ONLY when actual weighing would delay time-critical emergency interventions — specifically cardiac arrest, anaphylaxis, status epilepticus, or emergent airway management. Even in these scenarios, ask parents for the child's weight immediately (often known from recent clinic visits). Transition to measured weight as soon as the patient is stabilized. For all non-emergency situations, always measure actual weight before drug dosing. Never use estimated weight for ongoing medication management once the patient is stable.

The Broselow-Luten tape is a length-based pediatric resuscitation tool where the child's measured body length (from head to heel) corresponds to a color-coded weight range with pre-calculated drug doses. It is generally more accurate than age-based formulas (APLS) because it measures the child's actual size rather than using age as a proxy. The Broselow tape covers children up to ~36 kg (about 12 years). APLS formulas are used when a Broselow tape is unavailable or when the child exceeds the tape's range. Both tools should serve as cross-checks — if they significantly disagree, obtain actual weight.

For pediatric cardiac arrest (VF, pulseless VT, PEA, or asystole), the standard epinephrine dose is 0.01 mg/kg IV or IO using 1:10,000 concentration (0.1 mL/kg of 1:10,000, maximum single dose 1 mg). This is repeated every 3–5 minutes during resuscitation. A 10-fold epinephrine overdose (0.1 mg/kg) is one of the most dangerous pediatric medication errors — always verify the dose independently. For anaphylaxis, epinephrine IM (anterolateral thigh) using 1:1,000 concentration: 0.01 mg/kg, maximum 0.5 mg per dose.

The Luscombe and Owens formula is: Weight (kg) = 3 × age + 7 for children 1–12 years. It was derived from UK children in 2007 and provides better accuracy than classic APLS formulas in well-nourished Western populations. For a 5-year-old: APLS gives 18 kg (2×5+8), Luscombe-Owens gives 22 kg (3×5+7) — a 22% difference. For obese or well-nourished children, Luscombe-Owens typically matches actual weight more closely. Both formulas are used clinically; APLS is more widely known internationally, while Luscombe-Owens is often preferred in UK-trained emergency clinicians.