Paediatric Endotracheal Tube Size Calculator
Endotracheal tube size for children from age — Cole formula for uncuffed (age/4 + 4), Khine for cuffed (age/4 + 3.5) — with insertion depth at the lip (age/2 + 12), nasal depth, suction catheter and laryngoscope blade suggestions.
How it works
Uncuffed ID (mm) = age/4 + 4 (Cole); cuffed ID = age/4 + 3.5 (Khine); oral depth (cm) = age/2 + 12 or 3 × ID; nasal depth = age/2 + 15; neonates: depth = weight (kg) + 6
The paediatric airway narrows at the cricoid ring, so tube size is chosen to seal without pressure injury. Cole’s formula predicts the uncuffed internal diameter from age and is accurate to within half a size in about two thirds of children — which is why one size up and down are always prepared. Modern low-pressure, high-volume cuffed tubes (Microcuff) are now preferred in most children over neonatal size, using a half-size smaller than the uncuffed estimate, because they reduce tube exchanges and aspiration. Depth formulas are starting points: confirm by auscultation, capnography and chest X-ray (tip mid-trachea, between T1 and T3). For infants under one year and neonates, weight-based tables replace age formulas. The Broselow tape does the same job by length in emergencies.
Worked example
A 6-year-old: uncuffed 6/4 + 4 = 5.5 mm, cuffed 5.0 mm; depth 6/2 + 12 = 15 cm at the lip; 11 Fr suction catheter; Macintosh 2 blade.
Frequently asked questions
Cuffed or uncuffed in small children?
Current guidance (ERC, AHA) accepts cuffed tubes at all ages except perhaps premature neonates, provided cuff pressure is kept under 20–25 cmH₂O.
What if the child is unusually large or small?
Formulas by age assume average growth. For a very small child, size by weight or use a length-based tape; confirm with a leak test at 20–25 cmH₂O.
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Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.