π« Endotracheal Tube Size Calculator
Tube size and depth from age or weight.
For informational purposes only, not medical advice. Consult a healthcare professional.
Endotracheal tube size follows simple rules: children over 2 use uncuffed ID = age/4 + 4 (cuffed: age/4 + 3.5), so a 6-year-old takes 5.5 uncuffed or 5.0 cuffed; neonates size by weight; adults run 7.0-7.5 mm for women and 7.5-8.0 for men. Depth is about 3 Γ the ID in cm at the teeth. Calculate above.
How to Use This Calculator
Tube size is the internal diameter in millimeters. Pick the pathway that matches your patient; the calculator applies the standard formula for each.
For children 1 year and older, enter age. The calculator gives both uncuffed and cuffed sizes plus the depth estimate.
For neonates (age 0), enter weight in kg. Size follows weight bands: under 1 kg 2.5, 1-2 kg 3.0, 2-3 kg 3.5, over 3 kg 3.5-4.0.
For adults, select sex for the usual range. Then confirm placement clinically: bilateral breath sounds, chest rise, misting, and above all capnography.
The Formulas
The age/4 formulas (Cole's formula and its cuffed variant) estimate the cricoid ring diameter, the narrowest point of the pediatric airway. The 0.5 mm difference between cuffed and uncuffed accounts for the cuff's bulk: a cuffed tube one half-size smaller seals with the cuff instead of wedging the tube itself. Depth at 3 Γ ID keeps the tip mid-trachea, roughly 2-3 cm above the carina in most children; the neonatal 6 + weight rule is the NRP's quick bedside check. Broselow tape gives the same answers by length for children when age is unknown.
Worked Example
Six-year-old: uncuffed 6/4 + 4 = 5.5 mm, cuffed 6/4 + 3.5 = 5.0 mm, oral depth 3 Γ 5.5 = 16.5 cm at the teeth. Two-year-old: 2/4 + 4 = 4.5 uncuffed, 4.0 cuffed, depth 13.5 cm. Neonate 3.5 kg: 3.5-4.0 mm tube, depth 6 + 3.5 = 9.5 cm at the lip. Adult male: 7.5-8.0 mm, about 23 cm at the teeth. The calculator reproduces each of these. Note the depth rules are starting points: tall patients need more, and the final authority is the chest X-ray showing the tip 3-5 cm above the carina in adults.
Cuffed vs Uncuffed in Children
| Question | Current practice |
|---|---|
| Cuffed or uncuffed? | Cuffed increasingly preferred at all ages with low-pressure cuffs |
| Why the shift? | Fewer tube exchanges, better ventilation, less aspiration; modern cuffs are safer |
| Cuff pressure | Keep 20-25 cm HβO; check with manometer |
| Leak test | Audible leak at 20-25 cm HβO suggests correct size |
| Too small | Excessive leak, poor ventilation, aspiration risk |
| Too large | Airway trauma, subglottic stenosis risk |
The old teaching (uncuffed under 8 years) has faded as high-volume low-pressure cuffs proved safe in children; many centers now use cuffed tubes routinely, choosing the half-size-smaller formula. Either way, have one half-size larger and one half-size smaller open before laryngoscopy, because formulas estimate and anatomy decides. A tube that passes with a gentle leak at 20-25 cm HβO is right; one that wedges tight or leaks like a sieve gets exchanged. For airway-adjacent respiratory math, our FEV1/FVC interpreter covers spirometry, and our oxygenation index addresses the ventilation side. This calculator is an educational reference for clinicians and students; airway management is performed by trained providers with backup equipment ready.
Confirming Placement Never Changes
Size formulas get the tube; confirmation proves it is in the trachea. Continuous waveform capnography is the standard: persistent exhaled COβ with a proper waveform essentially rules out esophageal intubation. Add bilateral axillary breath sounds, symmetric chest rise, and condensation in the tube. The depth number then gets refined by chest X-ray. No formula, including this one, replaces that sequence, and every intubation kit should include capnography before the first attempt.
Special Situations
Burns and airway edema may need a smaller tube than the formula says; have downsizes ready. Pregnancy slightly increases airway edema: many anesthesiologists choose 0.5 mm smaller for obstetric airways. Morbid obesity does not change tube diameter (the cricoid is not bigger) but shortens the safe depth margin, so confirm early. Subglottic stenosis history means asking what size fit last time and starting there. Formulas are population averages; the patient's own airway history outranks all of them.
The Difficult Airway Backup Plan
Formulas assume a normal airway. When the exam suggests difficulty (limited mouth opening, short neck, small jaw, prior difficult intubation), the plan changes before drugs are given: video laryngoscopy as first choice, a bougie ready, supraglottic airway backup open, and a second skilled pair of hands in the room. Tube size may drop 0.5 mm when edema is expected. The formula still picks the starting size, but the difficult-airway algorithm picks the strategy, and no calculator replaces a proper airway assessment. Document the Mallampati score and neck mobility with every intubation note.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What size ET tube for a 6 year old?
5.5 mm uncuffed or 5.0 mm cuffed (age/4 + 4 and age/4 + 3.5), with oral depth about 16.5 cm at the teeth (3 Γ ID). Have half sizes up and down available.
What is the formula for pediatric ETT size?
Cole's formula: uncuffed ID = age/4 + 4 for children 2 and older. Cuffed: age/4 + 3.5. Both give internal diameter in mm. Depth β 3 Γ ID cm orally.
What size ET tube for adults?
Typically 7.0-7.5 mm ID for women and 7.5-8.0 mm for men, at about 21 cm (women) or 23 cm (men) at the teeth. Confirm tip position 3-5 cm above the carina on X-ray.
What size ET tube for a neonate?
By weight: under 1000 g 2.5 mm, 1000-2000 g 3.0 mm, 2000-3000 g 3.5 mm, over 3000 g 3.5-4.0 mm. Depth β 6 + weight(kg) cm at the lip.
How deep should an ET tube go?
Oral depth β 3 Γ tube ID in cm at the teeth for children; ~21-23 cm for adults. Nasal tubes sit 2-3 cm deeper. Final position is confirmed by chest X-ray.
Cuffed or uncuffed ETT for children?
Modern practice increasingly favors cuffed tubes at all pediatric ages with low-pressure cuffs (20-25 cm HβO), using the half-size-smaller formula. They reduce tube exchanges and aspiration.
How do you confirm ET tube placement?
Continuous waveform capnography first (persistent COβ with proper waveform), plus bilateral breath sounds, chest rise, and tube misting. Chest X-ray confirms depth. Never rely on a single sign.
What happens if the ET tube is too small?
Excessive air leak around the tube, inadequate ventilation pressures, aspiration risk, and the need for reintubation with a larger size. A leak at 20-25 cm HβO suggests correct sizing.
What is the 3x ID rule?
Oral ETT depth in cm β 3 Γ internal diameter in mm (e.g. 5.5 mm tube β 16.5 cm at the teeth). It positions the tip mid-trachea in most children; verify radiographically.
Does obesity change ET tube size?
No for diameter: the cricoid ring size does not grow with body weight, so the age/weight formulas still apply. Obesity shortens necks and reduces safe depth margins, so confirm placement promptly.