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Pediatric ETT size: the Cole formula, age ÷ 4 + 4

A pediatric ETT size estimate gives the internal diameter of an endotracheal tube from a child's age. This pediatric ETT size calculator uses the Cole 1957 formula for an uncuffed tube: age in years divided by 4, plus 4, in millimetres. It returns the result to one decimal place.

Not a medical device. Not a diagnosis or dosing recommendation.

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What is the Cole formula?

Cole's 1957 paper, "Pediatric formulas for the anesthesiologist", gave age-based arithmetic for an uncuffed tube's internal diameter. The calculator applies that one formula.

It accepts ages from 0.5 to 12 years. That range is a limit set by the calculator around typical pediatric use, not a rule from the paper.

The pediatric ETT size formula

ETT internal diameter (mm) = age (years) ÷ 4 + 4

result to 1 decimal place

Exact expression the calculator uses:

ett_id_mm = age_years / 4 + 4

Inputs

InputMeaningRange
age_yearsAge in years0.5 to 12

The response gives ett_id_mm, the uncuffed internal diameter in millimetres.

How the calculation works

  1. Divide the age in years by 4.
  2. Add 4.
  3. Round to one decimal place.

The calculator returns that number as it is. It doesn't round to the nearest tube size on a shelf.

Worked examples

These use Magent's own expected values for the calculator.

Example 1: age 4

  1. 4 ÷ 4 + 4 = 5.
  2. Internal diameter 5.0 mm.

Example 2: age 8

  1. 8 ÷ 4 + 4 = 6.
  2. Internal diameter 6.0 mm.

Example 3: age 1

  1. 1 ÷ 4 + 4 = 4.25.
  2. Rounded to one decimal place, internal diameter 4.3 mm.

History of the formula

Cole published "Pediatric formulas for the anesthesiologist" in 1957. The age ÷ 4 + 4 formula the calculator uses comes from that paper.

When it's used

When an age-based estimate of uncuffed tube diameter is wanted, for example in teaching or planning.

Where it's used

Anaesthesia, emergency care, intensive care and teaching.

Who uses it

Anaesthetists, emergency and intensive care clinicians, and students. The calculator does the arithmetic.

Limits of the calculation

  • It's an age-based estimate. It doesn't measure the child.
  • It applies the uncuffed Cole formula and no other.
  • It isn't a substitute for length-based tapes.
  • It doesn't pick a tube or round to a stock size.
  • Ages outside 0.5 to 12 years are rejected.

Clinical decisions belong to a qualified clinician who knows the patient.

  • Apgar score scores a newborn's condition shortly after birth; the Cole formula estimates a tube diameter from age.

Glossary

  • ETT: endotracheal tube, a tube placed into the windpipe.
  • Internal diameter (ID): the width of the inside of the tube, in millimetres.
  • Uncuffed: a tube without an inflatable cuff.

Common mistakes

  • Entering age in months. The input is in years; 6 months is 0.5.
  • Expecting a stock tube size. The calculator returns the formula's result to one decimal place.
  • Using it outside 0.5 to 12 years. Those ages are rejected.

Source

Cole F. Pediatric formulas for the anesthesiologist. AMA J Dis Child. 1957;94(6):672-673. DOI: 10.1001/archpedi.1957.04030070084009. PMID: 13478300

Frequently asked questions

What is the formula for pediatric ETT size?

The Cole formula: internal diameter in mm = age in years ÷ 4 + 4.

Is it for a cuffed or uncuffed tube?

The Cole formula is for an uncuffed tube.

Does the calculator round to a tube size?

No. It rounds to one decimal place and stops there.

What ages does it accept?

0.5 to 12 years.