Endotracheal Tube (ETT) Size Calculator
Select your patient group (adult, pediatric, or neonatal), enter age or weight, and get the recommended endotracheal tube (ETT) inner diameter for both cuffed and uncuffed tubes, plus the oral and nasal insertion depth in centimetres. Results are based on Cole's age-based formula for children, weight-based PALS guidelines for neonates, and standard adult sizing by sex.
How ETT size is calculated
For pediatric patients aged 1-12 years, the standard method is Cole's formula, developed by William Cole in 1957 and still widely used in emergency medicine and anesthesiology. The uncuffed formula is (age in years / 4) + 4; the cuffed formula is (age in years / 4) + 3.5. Both are rounded to the nearest 0.5 mm because commercial tubes are manufactured in 0.5 mm increments. For neonates and small infants, weight-based tables are used instead: 2.5 mm for babies under 1 kg, 3.0 mm for 1-2 kg, and 3.5 mm for 2-3 kg or above. Adult sizing is based on standard sex-based guidelines: 7.0-7.5 mm for females and 7.5-8.5 mm for males.
Cuffed versus uncuffed tubes
Historically, uncuffed tubes were the default for children under 8 years because the subglottic region forms a natural circular narrowing that acts as a functional seal, and older high-pressure cuffs risked damaging the tracheal mucosa. Modern low-pressure, high-volume cuffs have changed this picture: cuffed tubes are now preferred even in infants and toddlers in many settings because they reduce aspiration risk, improve ventilation control, and eliminate the need to change tubes when a leak develops. When a cuffed tube is used in children, the cuff pressure should be kept below 20-25 cmH2O to avoid ischaemia. Neonatal tubes remain uncuffed in nearly all protocols.
Insertion depth guidelines
A simple and widely taught rule for oral insertion depth is ETT inner diameter (mm) multiplied by 3. For example, a 5.0 mm tube should sit at approximately 15 cm at the lips. Nasal intubation adds roughly 2-3 cm. For adults, depth at the teeth is typically 21-23 cm for females and 22-24 cm for males. These are starting points only: definitive confirmation requires end-tidal CO2 capnography, bilateral chest auscultation, and a chest X-ray showing the tube tip 2-3 cm above the carina (at about the T2-T4 vertebral level). Tubes that are advanced too far enter the right main bronchus, causing right-sided ventilation only.
Clinical tips for tube selection
Always have the calculated size and one tube 0.5 mm smaller immediately at the bedside before any intubation attempt. If the selected tube passes the cords with a large audible air leak (more than 20-25 cmH2O), move up 0.5 mm. The patient's body habitus matters: obesity, short neck, and known subglottic stenosis may require a smaller tube. Pediatric formulas are age estimates and correlate imperfectly with actual tracheal diameter. In emergencies with an unknown-age child, height-based estimation using a Broselow tape or the Pedi-STAT app can cross-check the age estimate. For nasotracheal intubation, use the next size down from the oral estimate to navigate the narrower nasal passage.
ETT size quick reference by age and group
| Group / Age | Uncuffed ID (mm) | Cuffed ID (mm) | Oral depth (cm) |
|---|---|---|---|
| Neonate < 1 kg | 2.5 | N/A | 7.5 |
| Neonate 1-2 kg | 3.0 | N/A | 9 |
| Neonate 2-3 kg | 3.5 | N/A | 10.5 |
| Neonate > 3 kg | 3.5 | N/A | 10.5 |
| 1 year | 4.0 | 3.5 | 12 |
| 2 years | 4.5 | 4.0 | 13.5 |
| 4 years | 5.0 | 4.5 | 15 |
| 6 years | 5.5 | 5.0 | 16.5 |
| 8 years | 6.0 | 5.5 | 18 |
| 10 years | 6.5 | 6.0 | 19.5 |
| 12 years | 7.0 | 6.5 | 21 |
| Adult female | 7.0-7.5 (cuffed) | 7.0-7.5 | 21 |
| Adult male | 7.5-8.5 (cuffed) | 7.5-8.5 | 23 |
Pediatric sizes use Cole's formula rounded to the nearest 0.5 mm. Neonatal sizes are weight-based (PALS/NRP). Adult sizes are standard sex-based guidelines. Always have one size smaller available.
Frequently asked questions
What is the ETT size formula for a child?
The most widely used formula is Cole's: for an uncuffed tube, ETT size (mm ID) = (age in years / 4) + 4. For a cuffed tube, substitute 3.5 for the 4 at the end: (age / 4) + 3.5. Round the result to the nearest 0.5 mm. For example, a 4-year-old needs a 5.0 mm uncuffed or 4.5 mm cuffed tube.
What size ETT should I use for an adult?
Standard adult recommendations are 7.0-7.5 mm ID for female patients and 7.5-8.5 mm ID for male patients, always cuffed. A 7.5 mm tube is a common default for females and 8.0 mm for males when no other information is available. Always have a 0.5 mm smaller tube at hand in case the standard size does not pass easily.
How do I calculate oral insertion depth?
A reliable bedside rule is to multiply the ETT inner diameter (in mm) by 3. A 5.0 mm tube should be at approximately 15 cm at the lips; a 7.5 mm adult tube at approximately 22-23 cm. For nasal intubation, add about 2-3 cm to the oral depth estimate. Always confirm with capnography, auscultation, and a chest X-ray.
Should I use a cuffed or uncuffed tube in children?
Modern guidelines, including those from the American Heart Association PALS program, now accept cuffed tubes even in young children when the cuff pressure is kept below 20-25 cmH2O. Cuffed tubes reduce aspiration risk, improve ventilation, and prevent unnecessary tube changes. Uncuffed tubes are still used in neonates and some practitioners prefer them for infants under 1 year. In a trauma or critical care setting, a cuffed tube is typically preferred for any patient who needs reliable airway protection.
What ETT size is used for neonates?
Neonatal sizing is weight-based, not age-based: 2.5 mm for babies under 1 kg, 3.0 mm for 1-2 kg, and 3.5 mm for 2-3 kg and above (up to about 4 kg). Neonatal tubes are virtually always uncuffed. Oral insertion depth is approximately ETT size (mm) x 3, which gives 7.5-10.5 cm depending on weight.
Is Cole's formula accurate?
Cole's formula is a reliable starting estimate but it is not perfectly accurate for every patient. Studies comparing it with actual tracheal diameter measurements show it works well for most children but can be off by 0.5 mm in either direction. Height-based formulas and ultrasound measurement of the subglottic width can be more accurate when time and equipment allow. Always treat the result as a starting size, not an absolute value, and have 0.5 mm smaller and larger tubes available.