Why use it

Rapid estimation of appropriate tube size in pediatric emergencies. Essential for airway management preparation. Ensures correct equipment is ready before intubation attempt.

About

Estimates the appropriate uncuffed and cuffed endotracheal tube (ETT) size for pediatric patients based on age. Also calculates depth of insertion (lip-to-tip). These are ESTIMATES — always have one size above and below available. Cuffed tubes are now preferred in most settings.

When to use

Preparing for pediatric intubation
Equipment selection in pediatric emergency
Pre-procedural airway assessment

Formula

Uncuffed ETT (mm ID) = (Age in years / 4) + 4 Cuffed ETT (mm ID) = (Age in years / 4) + 3.5 Insertion depth (cm, oral) = 3 × ETT ID Alternative depth: (age/2) + 12 cm

Pearls & pitfalls

Cuffed ETTs are now preferred even in young children (AHA/PALS guidelines).
Uncuffed formula: (age/4) + 4. Cuffed formula: (age/4) + 3.5.
Neonates: term = 3.5 uncuffed (3.0 cuffed); preterm = 2.5-3.0.
Insertion depth (oral): 3 × ETT internal diameter (e.g., 4.0 tube → 12 cm at lip).
The little finger rule is unreliable — use the formula.
Always have suction, smaller tube, and LMA available as backup.

Next steps

Always have tubes 0.5 mm above and below calculated size available. Confirm placement with ETCO₂, bilateral breath sounds, and CXR. Use cuffed tubes with cuff pressure monitoring (< 20-25 cmH₂O). Secure tube at calculated insertion depth.

Evidence

Original formula by Cole (Anesthesiology, 1957). Modified over decades. AHA/PALS and ASA guidelines support cuffed tubes in children > 1 year. Formula accuracy: correct size in ~50-75% of cases — always prepare alternatives.

References

Kleinman ME et al. Pediatric Advanced Life Support: 2010 AHA Guidelines for CPR and ECC. Circulation. 2010;122(suppl 3):S876-S908. — link

Pediatric ETT Size

Calculator