Estimates the cuffed or uncuffed endotracheal tube size and oral insertion depth for a child from age.
Result
Enter the age and choose the tube type.
Sources
AHA 2020 · 4 studies
AHA 2020 Cuffed tubes are reasonable in infants and children.
4
studies
478
citations
380
PubMed papers
Evidence
Guideline recommendation
“The 2020 pediatric advanced life support guidelines state that it is reasonable to choose cuffed over uncuffed endotracheal tubes for intubating infants and children, with attention to tube size, position and cuff inflation pressure.”
American Heart Association
Circulation: Journal Metrics Score 2.3, Q2 · cited 1,359 times
Known limitations
In 488 children from term newborns to 8 years, randomized to cuffed tubes sized by age/4 + 3 or uncuffed tubes sized by age/4 + 4, the cuffed size was appropriate in 99% against 77% for uncuffed; croup was equally uncommon (about 1%) in both groups.
Anesthesiology: Journal Metrics Score 2.6, Q1 · cited 478 times
In 204 children from 1 day to 15 years, only 21% of the cuffed tubes chosen matched the Khine prediction, and 72% were larger; the authors proposed age/4 + 3.5 for children over 1 year.
Paediatr Anaesth: Journal Metrics Score 1.2, Q3 · cited 73 times
In 2,246 children under 5 years, cuffed tubes needed changing in 2.1% against 30.8% for uncuffed tubes, with similar post-extubation stridor (4.4% against 4.7%).
Br J Anaesth: Journal Metrics Score 4.1, Q1 · cited 362 times
Ultrasound measurement of the subglottic diameter predicted the tube size chosen clinically in 98% of cuffed and 96% of uncuffed intubations, better than age and height formulas.
Anesthesiology: Journal Metrics Score 2.6, Q1 · cited 236 times
The cuffed formula has been cited 478 times, and 380 PubMed articles mention pediatric endotracheal tube sizing in their title or abstract. Citation counts from OpenAlex and article counts from PubMed, retrieved November 13, 2026. Journal Metrics Scores and quartiles are from this site’s current release; follow the journal name for details.
Around intubation
Before intubation · After intubation · Special situations
Prepare more than one size. Confirm position and fit. Formulas are for typical children.
Next steps
Avoid common errors
5 common errors to avoid
and 3 more
When the formula misleads
1Age is only a proxy
Children of the same age differ in size; a small or large child may need a different tube. The formulas were studied in typical children.
2Cuffed sizes are smaller
A cuffed tube has a larger outer diameter than an uncuffed tube of the same internal size, which is why the cuffed formulas subtract 0.5 mm (Duracher) or 1 mm (Khine). With modern thin-walled cuffed tubes the difference in outer diameter is small.
3Manufacturers differ
Outer diameter and cuff position differ between brands of the same internal size. The trials used particular tubes.
4Depth needs checking
Depth formulas are estimates. A tube that is too deep enters a main bronchus; a tracheal bronchus can be blocked even at a usual depth.
5Newborns and adolescents
Newborns are sized by weight or gestation; preterm babies need smaller tubes; adolescents are sized by body size, as adults are.
Formula
Cuffed: age/4 + 3.5 from 1 year (age/4 + 3 under 1); uncuffed: age/4 + 4 from 2 years; oral depth age/2 + 12 cm.
age/4 + 3.5 (cuffed)
age/4 + 4 (uncuffed)
Cuffed: age/4 + 3.5 from 1 year (age/4 + 3 under 1); uncuffed: age/4 + 4 from 2 years; oral depth age/2 + 12 cm.
Formulas and quick reference
| Tube | Age | Formula |
|---|---|---|
| Cuffed (Khine) | under 1 year | age/4 + 3 |
| Cuffed (Duracher) | 1 year and older | age/4 + 3.5 |
| Uncuffed (Cole) | 2 years and older | age/4 + 4 |
| Oral depth at the lips | any age; 2 years and older | 3 × tube size (cm); age/2 + 12 (cm) |
| Age | Cuffed (mm) | Uncuffed (mm) | Oral depth (cm) |
|---|---|---|---|
| 1 year | 3.5 or 4.0 | – | 3 × size |
| 2 years | 4.0 | 4.5 | 13 |
| 4 years | 4.5 | 5.0 | 14 |
| 6 years | 5.0 | 5.5 | 15 |
| 8 years | 5.5 | 6.0 | 16 |
| 10 years | 6.0 | 6.5 | 17 |
Cole 1957
Khine 1997
Duracher 2008
Rounding
Test cases
3 published cases, each also a test case
3 published cases; the calculator reproduces every size.
Worked examples
A 4-year-old girl (16 kg) with a neck lymphangioma and a tracheal bronchus seen on her chest X-ray was intubated for surgery with a 5.0 mm uncuffed tube, fixed at 14 cm at the lip.
“intubated with a 5.0 mm internal diameter uncuffed endotracheal tube (ETT) fixed at 14 cm at the lip”
Cole’s formula gives 4/4 + 4 = 5.0 mm, and age/2 + 12 gives 14 cm, both as used. Here the tracheal bronchus arose about 1 cm above the carina, so a tube placed too deep could have blocked it; bronchoscopy confirmed the tip was clear of it.
Entered as: Age: 4 years; Tube type: Uncuffed.
Source: Sarkar ME et al., Indian J Anaesth 2018 (PubMed · Free full text · DOI)
A 7-year-old boy (25 kg) having a dental extraction was intubated through the nose with a 5.0 mm cuffed tube sized by the Duracher formula. A persistent leak from a faulty, lopsided cuff led to a change to a 5.5 mm tube, after which ventilation was normal.
“the nasotracheal tube size was determined using the Duracher formula (age/4 + 3.5). The appropriate size was determined as 5.0.”
Duracher gives 7/4 + 3.5 = 5.25 mm, between two sizes. The team took the smaller size, as is usual for nasal tubes, and the larger one was the replacement. The depth from this calculator is for oral tubes.
Entered as: Age: 7 years; Tube type: Cuffed.
Source: Park KN et al., J Dent Anesth Pain Med 2024 (PubMed · Free full text · DOI)
A 3-year-old boy with nephrotic syndrome developed plastic bronchitis with influenza A. The standard cuffed tube for his age was 4.5 mm, but the bronchoscope needed at least 5.0 mm, so the team deliberately used a 5.0 mm cuffed tube, removed the mucus plug and avoided ECMO.
“The standard cuffed tube size for the patient’s age had an inner diameter of 4.5 mm”
Duracher gives 3/4 + 3.5 = 4.25 mm, between 4.0 and 4.5; the team’s standard size was the larger. Going one size above that, as here, raises the risk of airway injury and needs close cuff pressure checks.
Entered as: Age: 3 years; Tube type: Cuffed.
Source: Gotou T et al., Cureus 2025 (PubMed · Free full text · DOI)
FAQ
6 questions and answers
and 4 more answers
Questions
For a cuffed tube, internal diameter (mm) = age in years ÷ 4 + 3.5 from 1 year (Duracher), or age ÷ 4 + 3 under 1 year (Khine). For an uncuffed tube from 2 years, age ÷ 4 + 4 (Cole). A 6-year-old gives 5.0 mm cuffed or 5.5 mm uncuffed.
Tubes come in half-millimeter steps but age ÷ 4 moves in quarter steps, so the formula often lands halfway between two sizes, as 4.25 mm does for a 3-year-old. The calculator then shows both. Teams differ on which to start with; either way, the other size should be ready.
Current resuscitation guidance favours cuffed tubes for intubating infants and children, with attention to tube size, position and cuff pressure. In a European trial of 2,246 children under 5, cuffed tubes needed far fewer tube changes (2.1% against 30.8%) without more stridor after extubation.
For an oral tube, a common estimate is 3 × the tube size in cm at the lips, or age ÷ 2 + 12 cm from 2 years. These are estimates: confirm with end-tidal CO₂, listening to both sides of the chest and a chest X-ray, and look for the depth mark on the tube at the vocal cords. Nasal tubes sit deeper.
Newborn tubes are usually chosen by weight or gestational age, from the neonatal resuscitation size chart in your unit, rather than by an age formula.
Measuring the subglottic diameter by ultrasound predicted the tube size chosen clinically more often than age and height formulas in one study. Length-based tapes, the child’s little finger and weight-based charts are also used. No method replaces checking the leak and having other sizes ready.
Further reading
9 references with PubMed and DOI links
9
references
3
free full text
From Khine HH et al., Anesthesiology 1997 to the newest case reports.
References
clinical grade of aneurysmal subarachnoid hemorrhage, I to V.
total calcium adjusted for albumin, in mg/dL or mmol/L.
stroke severity from 15 bedside items, 0 to 42.
MAP from systolic and diastolic pressure, against the 65 mm Hg target.
eye, verbal and motor scores for preverbal children, 3 to 15.
oxygenation ratio with the Berlin ARDS severity ranges.
serum sodium corrected for high glucose, Katz or Hillier factor.
sodium − (chloride + bicarbonate), with the albumin-corrected gap.
urea nitrogen to creatinine ratio, in US or SI units.
estimated creatinine clearance with actual, ideal or adjusted weight.
cardiac output and index from oxygen consumption and saturations.
ANC from the white cell count, neutrophils and bands.
insulin resistance from fasting glucose and insulin, in US or SI units.
FENa from plasma and urine sodium and creatinine: prerenal, indeterminate or tubular pattern.
three-item stroke severity screen for large vessel occlusion, 0 to 4.
water deficit in hypernatremia from sodium, weight and body water.
expected PaCO2 in metabolic acidosis, 1.5 × HCO3 + 8 ± 2.
corrected QT interval by Bazett, Fridericia, Framingham or Hodges.
head CT decision rule for children with minor head trauma.
blood loss before hemoglobin or hematocrit reaches a chosen lowest value.
eye, verbal and motor response, 3 to 15, with GCS-Pupils.
Devine ideal body weight and adjusted weight from height and sex.
calculated osmolality, osmolal gap and ethanol correction.
severity of alcohol-associated hepatitis from prothrombin time and bilirubin.
MELD, MELD-Na and MELD 3.0 for chronic liver disease.
early stroke risk after a transient ischemic attack.
Which published the Duracher study, with its current metrics.
Contributed by Dr. Meng Zhao (MD · Former Neurosurgeon · Medical AI Researcher), from the original publications listed here. Last updated November 13, 2026. LinkedIn
The calculator code is tested against every worked example on this page before each release.
This calculator supports, and does not replace, clinical judgment. It is meant for healthcare professionals and is not medical advice for patients. Report an error through the contact page.