Pediatric Calculators

Clinical calculators for pediatric medicine

Age → Weight estimator
Estimator only — copy the weight into whichever calculator you need.
Weight-estimation formulas
APLS (Luscombe & Owens 2007 / APLS-UK 2016)
• 0-12 months: (0.5 × age in months) + 4
• 1-5 years: (2 × age in years) + 8
• 6-12 years: (3 × age in years) + 7
Best Guess (Tinning & Acworth 2007)
• 1-11 months: (age in months + 9) / 2
• 1-4 years: 2 × (age in years + 5)
• 5-14 years: 4 × age in years
Broselow tape (length-based) is most accurate when available.

Blood Pressure Percentile

AAP 2017 Clinical Practice Guideline

Based on normative tables for normal-weight children ages 1-17. Flynn et al., Pediatrics 2017;140(3):e20171904.

Definitions: Hypertension & Hypotension (AAP 2017 / Nelson)

Hypertension Classification (AAP 2017)

CategoryAges 1 to <13 yearsAges ≥13 years
Normal<90th percentile<120/<80 mmHg
Elevated BP≥90th to <95th percentile
OR 120/80 mmHg to <95th (whichever lower)
120-129/<80 mmHg
Stage 1 HTN≥95th percentile to <95th + 12 mmHg
OR 130/80-139/89 mmHg (whichever lower)
130/80 to 139/89 mmHg
Stage 2 HTN≥95th + 12 mmHg
OR ≥140/90 mmHg (whichever lower)
≥140/90 mmHg

Hypertensive Urgency vs Emergency (Nelson)

  • Hypertensive urgency: Severe BP elevation (>95th + 30 mmHg or >180/120) WITHOUT end-organ damage. Requires reduction over 24-48 hours.
  • Hypertensive emergency: Severe BP elevation WITH end-organ damage (encephalopathy, heart failure, retinopathy, renal injury). Requires immediate IV therapy with goal reduction of 25% in first 8 hours.

Hypotension (AAP/PALS)

  • Definition: Systolic BP below the 5th percentile for age, sex, and height.
  • Quick estimate (1-10 years): Hypotension = SBP < 70 + (2 × age in years) mmHg
  • Neonates: SBP < gestational age in weeks (term: <60 mmHg)
  • Clinical significance: Hypotension in children is a late sign of shock. Tachycardia, poor perfusion, and altered mental status typically precede hypotension.

Sources: Flynn JT et al., Pediatrics 2017;140(3). Nelson Textbook of Pediatrics, 21st ed. PALS Provider Manual.