This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Choosing the right tube quickly
When a child needs a breathing tube, the team has seconds to pick a size. A tube too large can injure the airway; one too small leaks and makes ventilation difficult. Because a child’s airway grows with age, simple formulas give a good first estimate for children aged 1 year and older.
The formulas
- Cuffed tube: internal diameter (ID) = age ÷ 4 + 3.5 mm.
- Uncuffed tube: ID = age ÷ 4 + 4 mm.
- Depth at the lips: about 3 × ID, or age ÷ 2 + 12 cm.
- Depth at the nostril for a nasal tube: age ÷ 2 + 15 cm.
- Suction catheter: about 2 × the ID, in French (Fr) units.
The calculator rounds tube sizes to the nearest half millimeter, since tubes come in 0.5 mm steps.
Example for a 4-year-old
- Cuffed tube: 4 ÷ 4 + 3.5 = 4.5 mm.
- Uncuffed tube: 4 ÷ 4 + 4 = 5.0 mm.
- Oral depth: 4 ÷ 2 + 12 = 14 cm, or 3 × 4.5 = 13.5 cm.
- Nasal depth: 4 ÷ 2 + 15 = 17 cm.
- Suction catheter: 10 Fr.
Younger and older children
| Age | Usual uncuffed ID | Usual cuffed ID |
|---|---|---|
| Preterm newborn | 2.5 to 3.0 mm | not usually used |
| Term newborn | 3.0 to 3.5 mm | 3.0 mm |
| 1 to 12 months | 3.5 to 4.0 mm | 3.0 to 3.5 mm |
| 2 years | 4.5 mm | 4.0 mm |
| 6 years | 5.5 mm | 5.0 mm |
| 10 years | 6.5 mm | 6.0 mm |
Below age 1 the formulas are not reliable, and teams use weight or gestational age instead. Teenagers move toward adult sizes, typically 6.0 to 7.0 mm for girls and 7.0 to 8.0 mm for boys.
Cuffed tubes
For decades, uncuffed tubes were standard in young children because of fears of airway damage. Modern low-pressure cuffs changed that, and current resuscitation guidelines, including those of the American Heart Association, accept cuffed tubes in infants and children provided the cuff pressure is kept below about 20 to 25 cm H₂O.
Always confirm
A formula is a starting point. Have tubes half a size larger and smaller ready, check the size against a length-based tape when available, and confirm placement with end-tidal CO₂, chest rise, breath sounds and a chest X-ray. Secure the tube and recheck the depth after every move of the patient.