Endotracheal Tube (ETT) Size Calculator

Estimate the right endotracheal tube internal diameter (ID, mm) and oral insertion depth from age, weight, sex, and tube type — using the standard Cole, Khine, and NRP guideline formulas.

⚠️ Educational estimates only. These formulas are starting estimates, not clinical decisions. Final airway decisions — including tube size, cuff choice, and depth — must be made by a qualified anesthesiologist or clinician. Always have one size above and below the estimate ready.

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⚠️ Estimate for educational purposes. Airway decisions are made by the anesthesiologist at the bedside. Verify tube position clinically and radiographically.

Worked example

4-year-old, cuffed tube: ID = 4 ÷ 4 + 3 = 4.0 mm; keep 3.5 mm and 4.5 mm ready (±0.5 mm). Oral depth ≈ 3 × 4.0 = 12 cm at the teeth.

Reference formulas & tables

Children (age-based)

Formula	Tube	Example
ID (mm) = age ÷ 4 + 4	Uncuffed (Cole)	8-yr-old → 6.0 mm; depth 3 × 6.0 = 18 cm
ID (mm) = age ÷ 4 + 3	Cuffed (Khine)	6-yr-old → 4.5 mm; depth 3 × 4.5 = 13.5 cm

Newborns (weight-based, NRP)

Weight	ID	Depth at lips ≈ weight + 6
Below 1.0 kg	2.5 mm	0.8 kg → 2.5 mm, ≈ 7 cm
1.0–2.0 kg	3.0 mm	1.5 kg → 3.0 mm, ≈ 7.5 cm
2.0–3.0 kg	3.0 mm (prepare 3.5)	2.5 kg → 3.0 mm, ≈ 8.5 cm
Above 3.0 kg	3.5 mm	3.5 kg → 3.5 mm, ≈ 9.5 cm

Adults (oral intubation reference)

Group	Recommended ID	Usual range	Depth at teeth
Female	7.5 mm	7.0–8.0 mm	≈ 21 cm
Male	8.0 mm	7.5–8.5 mm	≈ 23 cm

Sources: Cole formula / Khine et al., Anesthesiology 1997; AAP Neonatal Resuscitation Program Table 5-1; McGraw-Hill anesthesia text. Full citations in the tool's SOURCES file. Sizes come in 0.5 mm increments; results are rounded to the nearest available tube.

Frequently asked questions

What does this endotracheal tube size calculator estimate?

It estimates the internal diameter (ID, in mm) of the endotracheal tube and the oral insertion depth from the patient's age, weight, sex, and tube type. The output is a starting estimate for education and preparation — the final choice is always made by the anesthesiologist at the bedside.

How is pediatric ETT size calculated?

For children the standard age-based formulas are used: uncuffed tubes follow Cole's formula ID = age ÷ 4 + 4, and cuffed tubes follow the Khine formula ID = age ÷ 4 + 3. For example, a 4-year-old with a cuffed tube: 4 ÷ 4 + 3 = 4.0 mm ID, with an estimated oral depth of 3 × 4.0 = 12 cm. Always keep one size above (4.5 mm) and one below (3.5 mm) ready.

What ETT size should be used for newborns?

Newborn tube size is weight-based per the Neonatal Resuscitation Program: below 1.0 kg → 2.5 mm; 1.0–2.0 kg → 3.0 mm; 2.0–3.0 kg → 3.0 mm (prepare 3.5 mm as well); above 3.0 kg → 3.5 mm. Insertion depth at the lips is approximately weight (kg) + 6 cm — for example a 1.5 kg newborn → 3.0 mm tube at about 7.5 cm.

What ETT size is used for adults?

For oral intubation, 7.5 mm ID is typical for an average woman (usual range 7.0–8.0 mm) and 8.0 mm ID for an average man (usual range 7.5–8.5 mm). Typical depth at the teeth is about 21 cm for women and 23 cm for men. Actual size is adjusted for height, body habitus, the procedure, and any airway disease.

How is ETT insertion depth estimated?

For children, oral depth at the teeth or lips is estimated as 3 × the tube ID — e.g. a 6-year-old with a 4.5 mm cuffed tube → 3 × 4.5 = 13.5 cm. For adults the traditional reference is about 21 cm (women) and 23 cm (men) at the central incisors. Nasal intubation is typically about 2–3 cm deeper than oral. Always confirm position clinically.

Can I use this for a real intubation?

No — this is an educational planning aid, not medical advice. Formulas estimate an average airway; individual anatomy varies widely. Airway decisions must be made by a qualified anesthesiologist or clinician, who will confirm tube position with clinical signs, capnography, and usually a chest radiograph. Have a tube one size larger and one size smaller immediately available.

Endotracheal Tube (ETT) Size Calculator

Calculator

Result

Worked example

Reference formulas & tables

Children (age-based)

Newborns (weight-based, NRP)

Adults (oral intubation reference)

Frequently asked questions

What does this endotracheal tube size calculator estimate?

How is pediatric ETT size calculated?

What ETT size should be used for newborns?

What ETT size is used for adults?

How is ETT insertion depth estimated?

Can I use this for a real intubation?

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