A 6-year-old has been brought in unresponsive from a witnessed seizure. The parents are distressed and cannot provide the child's weight. Before any drug calculations can proceed, the crew needs an estimated weight from the child's age so that adrenaline, atropine and fluid bolus volumes can be confirmed.
Paeds Weight Estimator (Broselow)
Paediatric
Infant (<1 yr): (age months + 9) ÷ 2
1–5 yrs: (age × 2) + 8
6–12 yrs: (age × 3) + 7
The Broselow tape uses measured length as a proxy for weight, colour-coded to pre-calculated drug doses. Use actual weight whenever possible.
💡 These are estimates only. Actual weight should be obtained as soon as practicable. All doses must be verified against your clinical practice guidelines before administration.
Clinical safety:
🇦🇺 Verify with facility drug formulary and senior clinician · Meets AHPRA/ACSQHC standards
1 What this calculator does
Estimates paediatric patient weight using age-based APLS formulas or length-based Broselow approximation. Shows the weight estimate alongside calculated emergency drug doses for adrenaline (0.01 mg/kg), atropine (0.02 mg/kg), paracetamol (15 mg/kg) and IV fluid bolus (20 mL/kg). All doses are illustrative -- verify with protocol before administration.
2 Formula & professional reasoning
Age-based weight estimation (APLS formulas):
Infant <1 year: (Age in months + 9) / 2 kg
Child 1-5 years: (Age in years x 2) + 8 kg
Child 6-12 years: (Age in years x 3) + 7 kg
Length-based (Broselow approximation):
Weight kg = (Length cm x 0.1756) - 1.556 (minimum 3 kg)
Applies to patients up to approximately 36 kg / 143 cm length
Accurate weight estimation is critical for safe paediatric drug dosing. The APLS age-based formulas provide a rapid estimate when actual weight is unavailable. The Broselow length-based system is more accurate than age-based formulas and provides a colour-coded reference for precalculated drug doses and equipment sizes. The Broselow tape is considered the gold standard prehospital paediatric weight estimation tool, with studies showing it outperforms age-based estimates across all age groups. Both systems are less accurate in obese or underweight children.
3 Worked examples
⚠️ Illustrative example only — not clinical or professional instruction.
Basic
6-year-old -- age-based APLS formula
Given: Age: 6 years | Method: age-based | APLS formula: 6-12 years
Working:
Weight estimate: (6 x 3) + 7 = 18 + 7 = 25 kgAnswer: Estimated weight: 25 kg | Adrenaline 0.01 mg/kg: 0.25 mg = 2.5 mL (1:10,000) | Atropine 0.02 mg/kg: 0.50 mg | Paracetamol 15 mg/kg: 375 mg | Fluid bolus 20 mL/kg: 500 mL
💡 Illustrative example only. Verify all clinical decisions with your agency protocol, medical director and partner clinician. Meets AHPRA/ACSQHC prehospital care standards. These are illustrative calculated doses from the estimated weight. All doses must be verified against your agency's paediatric drug protocol before administration. Use actual weight when available. If the child appears significantly larger or smaller than average, adjust the estimate accordingly.
Standard
Infant 8 months -- APLS infant formula
Given: Age: 8 months (0 years 8 months) | Method: age-based | APLS formula: <1 year
Working:
Weight estimate: (8 months + 9) / 2 = 17 / 2 = 8.5 kgAnswer: Estimated weight: 8.5 kg | Adrenaline 0.01 mg/kg: 0.085 mg = 0.85 mL (1:10,000) | Atropine 0.02 mg/kg: 0.17 mg | Paracetamol 15 mg/kg: 127.5 mg | Fluid bolus 20 mL/kg: 170 mL
💡 Illustrative example only. Verify all clinical decisions with your agency protocol, medical director and partner clinician. Meets AHPRA/ACSQHC prehospital care standards. Infant drug volumes are small and precise measurement is critical. In an 8.5 kg infant, 0.85 mL of adrenaline 1:10,000 is the estimated dose -- use a 1 mL syringe for accurate measurement. Verify with the Broselow tape if available.
Advanced
Length-based Broselow estimate -- 115 cm child
Given: Length: 115 cm | Method: length-based (Broselow)
Working:
Weight: (115 x 0.1756) - 1.556 = 20.194 - 1.556 = 18.64 kg | Rounded: 18.6 kgAnswer: Estimated weight: 18.6 kg | Adrenaline 0.01 mg/kg: 0.186 mg = 1.86 mL (1:10,000) | Fluid bolus 20 mL/kg: 372 mL
💡 Illustrative example only. Verify all clinical decisions with your agency protocol, medical director and partner clinician. Meets AHPRA/ACSQHC prehospital care standards. A length of 115 cm corresponds approximately to a 7-8 year old. The Broselow approximation gives 18.6 kg -- similar to the APLS formula result for a 7-year-old ((7x3)+7 = 28 kg -- actually differs, showing the value of having both methods). Use actual Broselow tape for colour-band based dosing where available.
4 Sanity check
APLS weight formulas by age group
Infant <1yr: (months+9)/2 | Child 1-5yr: (age x 2)+8 | Child 6-12yr: (age x 3)+7
These formulas apply to children of average build. Overweight or underweight children will have proportionally different actual weights.
Broselow tape applies up to 36 kg or 143 cm
Above 36 kg or 143 cm: use adult weight estimation or scale | Below 46 cm: outside Broselow range -- check measurement
Always document that weight is estimated
Record the estimated weight, the estimation method used, and the note 'ESTIMATED' clearly in the patient record
Emergency doses shown are illustrative only
The displayed drug doses are calculated from the estimated weight using standard weight-based dosing formulas -- they are reference figures only and must be verified against your agency protocol before administration
5 Common errors
| Error | Cause | Consequence | Fix |
|---|---|---|---|
| Using the estimated weight as if it were a measured weight | Not clearly differentiating estimated from measured weight in documentation | Receiving hospital may use an inaccurate weight for subsequent drug dosing | Always document clearly: 'Estimated weight 25 kg by APLS formula (6-year-old)' or 'Estimated weight 18 kg by Broselow 115 cm'. Use the abbreviation 'Est.' or 'ESTIM' beside the weight in the patient record. Where possible, use a set of EMS scales for actual weight. |
| Applying the APLS age-based formula beyond 12 years | Treating the formula as applicable to all paediatric ages | Significant underestimation of weight in adolescents -- 13-16 year olds are not adequately represented by the APLS formulas | The APLS formulas apply from birth to 12 years only. For adolescents (13+ years) or children approaching adult size, use adult estimation methods or the Broselow tape if length is under 143 cm. Beyond Broselow range, use the adult weight estimation approach. |
| Not applying the Broselow minimum weight of 3 kg | Using the formula for very small infants or premature neonates | Calculated weight below 3 kg -- below the range of the Broselow system and below safe application of standard dose formulas | The Broselow system has a minimum applicable weight of 3 kg (approximately 46 cm length). For neonates and premature infants below this, use NICU/NETS-specific neonatal dosing and consult medical direction. Do not extrapolate the adult formulas to tiny infants. |
| Calculating drug doses directly from the estimated weight without a second clinician verification | Treating the estimated weight and calculated dose as final without checking | Weight estimation error compounded by calculation error -- cumulative risk of significant paediatric medication error | Paediatric weight-based drug calculations in the prehospital setting require independent double-check by the second clinician. The person who calculated the dose should not be the person who confirms it. Both clinicians should agree on the weight estimate, the dose in mg/kg and the final volume before administration. |
6 Reference & regulatory links
🇦🇺 Australia
7 Professional workflow
Common tools used alongside this one:
Cardiac Arrest Drug Doses
Cardiac Arrest Drug Doses uses the estimated weight for paediatric adrenaline and amiodarone dose calculation in cardiac arrest
→
APGAR Score
APGAR Score may be needed for neonates -- Paeds Weight Estimator handles older infants and children once neonatal period has passed
→