Pediatric Endotracheal Tube (ETT) Size

Estimate pediatric uncuffed and cuffed endotracheal tube internal diameter from age using Cole and Motoyama-style relationships, with insertion depth helpers and under-two age-band context. Educational tool.

Pediatric Endotracheal Tube (ETT) Size

Enter the patient's age in years to estimate uncuffed and cuffed ETT internal diameter and approximate insertion depth at the lip. Always confirm fit at the bedside; for emergencies, length-based tools (such as a Broselow tape) are preferred over age-based estimates when available.

Patient age

Age (years)

Decimals accepted (e.g. 0.5 for 6 months). Range 0 to 18 years.

Disclaimer: This calculator provides an estimate of pediatric ETT size from age. It does not replace bedside assessment, length-based emergency resuscitation tools, weight-based sizing, or the judgment of an experienced airway clinician. Always have tubes one size larger and one size smaller available.

Pediatric ETT size: formulas, age-based table, and clinical context

Overview

Pediatric airway anatomy changes rapidly with age, so endotracheal tube (ETT) size is estimated rather than fixed. Two age-based formulas are most commonly cited at the bedside: Cole's formula for uncuffed tubes and the Motoyama formula for cuffed tubes. Both estimate the internal diameter (ID) in millimetres for children at or above two years of age. For neonates, infants, and toddlers under two years, age-band sizing is more reliable because the formulas were not derived in this population.

Formulas

Tube	Formula (mm internal diameter)	Source
Uncuffed	(age in years / 4) + 4	Cole, 1957
Cuffed (modern)	(age in years / 4) + 3.5	Motoyama, 1996
Insertion depth at lip (oral)	ETT internal diameter x 3	Standard pediatric airway practice
Alternate depth (age 2+)	(age in years / 2) + 12	Standard pediatric airway practice

ETTs are commercially available in 0.5 mm increments. The recommended value is rounded to the nearest 0.5 mm. Always have one size larger and one size smaller available.

Age-band sizing for children under 2 years

Age band	Uncuffed (mm ID)	Cuffed (mm ID)
Premature (under ~2.5 kg)	2.5 to 3.0	Generally not used
Term newborn	3.0 to 3.5	3.0
Infant under 6 months	3.5	3.0
Infant 6 to 12 months	3.5 to 4.0	3.0 to 3.5
Toddler 1 to 2 years	4.0 to 4.5	3.5

Worked examples

4-year-old child

Uncuffed: (4 / 4) + 4 = 5.0 mm
Cuffed: (4 / 4) + 3.5 = 4.5 mm
Depth at lip (uncuffed x 3): 5.0 x 3 = 15 cm
Depth alternative: (4 / 2) + 12 = 14 cm

8-year-old child

Uncuffed: (8 / 4) + 4 = 6.0 mm
Cuffed: (8 / 4) + 3.5 = 5.5 mm
Depth at lip (uncuffed x 3): 6.0 x 3 = 18 cm
Depth alternative: (8 / 2) + 12 = 16 cm

9-month-old infant

Use the age-band recommendation: typically 3.5 to 4.0 mm uncuffed (or 3.0 to 3.5 mm cuffed). The Cole and Motoyama formulas are not validated below 2 years.

Practical tips

Always prepare three tube sizes: estimated, one half-size smaller, and one half-size larger. Pediatric airway anatomy varies, and the first attempt should not be the only attempt.
For emergency resuscitation in children under 35 kg, length-based estimation (Broselow tape or equivalent) is generally preferred to age-based formulas.
Cuffed tubes have become standard in children of most ages, including infants, when modern low-pressure, high-volume cuffs are used. Confirm cuff pressure is below 20 to 25 cm H2O after placement.
Confirm placement with bilateral chest rise, equal breath sounds, end-tidal CO2, and a chest x-ray. Auscultate for an audible leak around the tube at peak inspiratory pressures of 20 to 30 cm H2O for uncuffed tubes.
Reassess depth after positioning the child; tube tip can move significantly with neck flexion or extension.

Limitations

Age-based formulas are estimates only. Body habitus, congenital airway anomalies, syndromic features, and prior airway surgery can substantially change the optimal tube size.
The Cole and Motoyama formulas were derived in children at or above 2 years; they over- or under-estimate sizes in infants and toddlers, where age-band tables remain the standard.
For cuffed tubes, some authors prefer the alternative formula (age / 4) + 3 (Khine, 1997). Local protocol and tube manufacturer recommendations should guide selection.
Length-based emergency tools (such as the Broselow tape) outperform age-based estimation in resuscitation and should be used when available.

Key references

Cole F. Pediatric formulas for the anesthesiologist. AMA J Dis Child. 1957;94:672-673.
Motoyama EK. Endotracheal intubation. In: Motoyama EK, Davis PJ, eds. Smith's Anesthesia for Infants and Children. 5th ed. St. Louis: Mosby; 1990:269-275.
Khine HH, Corddry DH, Kettrick RG, et al. Comparison of cuffed and uncuffed endotracheal tubes in young children during general anesthesia. Anesthesiology. 1997;86(3):627-631.
American Heart Association. Pediatric Advanced Life Support (PALS) Provider Manual.
Teaching calculator: MDCalc: Pediatric Endotracheal Tube (ETT) Size

Practice caveats

The numeric estimate is a starting point only. Verify with capnography, breath sounds, chest rise, and an appropriate cuff leak.
In neonates and small infants, slight differences in tube size translate into large changes in airway resistance and air leak. Have a smaller tube ready and a clinician experienced in neonatal and infant intubation.
Always integrate this estimate with local guidelines, the patient's clinical picture, and institutional airway protocols.

Purpose and scope

Selecting an appropriate endotracheal tube (ETT) in children is an estimation exercise. Airway caliber changes quickly with growth, and clinical factors such as body habitus, congenital anomalies, prior airway surgery, or acute pathology can shift the optimal size away from any simple rule. This calculator encodes widely taught age-based relationships used to choose uncuffed and cuffed tube internal diameter (ID) in millimetres, approximate insertion depth at the lips in centimetres, and conventional rounding to the 0.5 mm increments that manufacturers supply.

The estimates here support teaching and structured bedside preparation. They do not replace trained procedural judgment, institutional protocols, direct visualization of tube fit, capnographic confirmation, or imaging when indicated.

Why tube size matters in pediatrics

In small patients, small changes in internal diameter produce disproportionate changes in airway resistance because resistance varies inversely with the fourth power of radius for laminar flow in a tube model. An oversized tube risks mucosal injury, mainstem bronchial intubation, or poor distal positioning; an undersized tube may cause inadequate ventilation, large leaks that interfere with oxygenation and ventilation monitoring, or higher work of breathing if spontaneous efforts persist. For uncuffed tubes, clinicians often listen for a small inspiratory leak at moderate ventilator pressures; for cuffed tubes, cuff pressure must be titrated after placement, commonly targeting roughly 20 to 25 cm H₂O when using modern low-pressure cuffs, per local practice.

Cuffed versus uncuffed tubes

Historically, uncuffed tubes dominated pediatric practice because of concern about subglottic injury from cuffs in narrow airways. Contemporary pediatric anesthesia and acute care increasingly use cuffed tubes across many ages when appropriate microcuff designs and careful cuff pressure management are used. Your choice should follow department policy, patient size and pathology, and whether controlled ventilation and precise airway protection are priorities.

This tool reports both uncuffed and cuffed estimates so teams can compare starting points side by side rather than assuming one tube type for every scenario.

Age-based formulas for children at or above two years

For children two years of age and older, two familiar formulas estimate internal diameter in millimetres:

Uncuffed (Cole relationship): ID (mm) = (age in years ÷ 4) + 4
Cuffed (Motoyama relationship): ID (mm) = (age in years ÷ 4) + 3.5

These relationships provide a continuous estimate across school-aged children and adolescents up to the upper bound used by the calculator. They were not derived for neonates or young toddlers, so treating them as definitive in infants will mis-track recommended sizes that come from developmental airway norms rather than from those regression-style expressions.

Insertion depth at the lips

Depth targets help reduce blind repositioning after intubation. Two common teaching constructs appear together because they sometimes diverge slightly, which prompts clinicians to reassess with visualization and imaging:

ETT diameter rule: depth at the lips (cm) ≈ ETT internal diameter (mm) × 3
Age rule for ages two years and older: depth at the lips (cm) ≈ (age in years ÷ 2) + 12

When two estimates disagree, neither should override continuous reassessment of tube tip position using clinical markers (chest rise, breath sound symmetry, capnography waveform quality) and radiography when appropriate. Neck flexion and extension materially change tip depth relative to the carina in children.

Neonates, infants, and toddlers under two years

Below age two, standardized age-band ranges reflect contemporary bedside norms more faithfully than extrapolating Cole or Motoyama downward. Typical teaching bands include the following starting points (always individualized):

Age band	Uncuffed ID (mm)	Cuffed ID (mm)
Premature or very low weight infants	Often 2.5 to 3.0	Often deferred or highly selective
Term newborn	Often 3.0 to 3.5	Often near 3.0 when used
Infant under six months	Often near 3.5	Often near 3.0
Infant six to twelve months	Often 3.5 to 4.0	Often 3.0 to 3.5
Toddler one to two years	Often 4.0 to 4.5	Often near 3.5

Cuffed tube use in neonates remains protocol-dependent; many teams prefer uncuffed tubes under roughly 3.5 kg, while others use cuffs routinely with strict pressure surveillance.

Rounding and equipment readiness

Commercial paediatric ETTs are stocked in 0.5 mm steps. Rounding the computed millimetre estimate to the nearest 0.5 mm aligns the number with supply on the cart. Standard preparation includes the predicted size plus one half-size below and one half-size above, because first-pass fit should not exhaust the airway plan.

Emergency resuscitation and length-based systems

In urgent pediatric airway management, especially for patients under conventional Broselow-style weight breakpoints, length-based tape systems map colour zones to suggested tube sizes and equipment. These systems frequently outperform isolated age recall during stress and reduce cognitive load. When a Broselow or equivalent resource is available, it is reasonable to prefer it for initial equipment selection and use age-based formulas as a cross-check rather than the reverse.

After intubation: confirmation and initial stabilization

Placement verification blends waveform capnography, auscultation, and clinical correlation. Initial ventilation targets are age-dependent; teaching scripts often cite tidal volumes near 6 to 8 mL per kg with respiratory rates higher in younger children, fraction of inspired oxygen titrated after oxygenation assessment, head elevation when feasible, gastric decompression when clinically appropriate, and arterial or venous blood gas sampling within a clinically relevant window after establishing controlled ventilation.

Limitations inherent to any estimator

Age-only models omit weight, height, sex, syndromic diagnosis, subglottic stenosis, tracheomalacia, burns, cervical spine precautions, and baseline respiratory mechanics. Some centres teach variant cuffed sizing slopes such as adding 3 rather than 3.5 to age divided by four under specific patient subsets. Always reconcile calculator output with manufacturer charts, specialty consultation when available, and direct assessment of leak, pressures, and ventilation efficacy.