What is the Cole formula?

The Cole formula estimates uncuffed ETT internal diameter as (age in years / 4) + 4 mm. It is the most widely cited pediatric ETT sizing formula and provides a starting estimate for children aged 1–12 years.

What is the Motoyama formula?

The Motoyama formula estimates cuffed ETT internal diameter as (age in years / 4) + 3.5 mm — 0.5 mm smaller than Cole to account for the cuff adding effective diameter at the tracheal wall. It is the standard recommendation when using cuffed tubes in children.

Should I use a cuffed or uncuffed tube for a child under 8?

Historically, uncuffed tubes were preferred for children under 8 because the subglottic cricoid ring was considered the narrowest point and a natural seal. Current evidence and the 2023 Difficult Airway Society pediatric guidelines support cuffed tubes at all ages (including neonates) when cuff pressure is monitored and kept below 20–25 cmH₂O, as they reduce reintubation rates and gas leak.

How do I size an ETT for a neonate?

For neonates, age-based formulas do not apply. This calculator uses weight-based sizing: less than 1 kg → 2.5 mm ID; 1–2 kg → 3.0 mm ID; 2–3 kg → 3.0–3.5 mm ID; greater than 3 kg → 3.5 mm ID. Insertion depth at lip (cm) approximates 6 + weight (kg).

What tube sizes should I have at the bedside?

Always prepare the calculated size plus one size larger and one size smaller (±0.5 mm ID). Anatomical variation, subglottic narrowing, and tube brand differences mean the first choice may not pass easily or may leak significantly.

How is insertion depth estimated?

A common estimate for oral insertion depth at the lip is 3× the ETT internal diameter (in cm) for children, or 6 + weight (kg) for neonates. This calculator displays this estimate; confirm with clinical landmarks, bilateral breath sounds, and chest X-ray.

Endotracheal Tube Size Calculator

Name: Endotracheal Tube Size Calculator
Availability: InStock
Author: Nham Vu

Enter patient age (or weight for neonates) to get the recommended ETT internal diameter using the Cole and Motoyama formulas, for both cuffed and uncuffed tubes.

Patient Parameters

Patient Type

Age (years, 1–16)

Tube Type

Uncuffed = Cole formula | Cuffed = Motoyama formula

Clinical note: These are starting estimates only. Always prepare ±0.5 mm sizes and confirm tube position by capnography, auscultation, and chest rise.

Recommended ETT

Enter patient details on the left to see the recommendation.

Summary

Enter patient age (or weight for neonates) to get the recommended ETT internal diameter using the Cole and Motoyama formulas, for both cuffed and uncuffed tubes.

How it works

Select the patient type: neonate (by weight) or child (by age in years).
Enter the patient's age in years (1–16) or weight in kilograms for neonates.
Choose uncuffed (standard for children under 8) or cuffed (preferred for children 8 and older, and all neonates in modern practice).
The calculator applies the Cole formula for uncuffed tubes and the Motoyama formula for cuffed tubes.
Recommended tube sizes (±0.5 mm) and suggested insertion depth at the lip are displayed.
Always confirm position by auscultation, capnography, and chest rise before securing the tube.

Use cases

Pre-operative ETT size selection for pediatric surgical cases.
Emergency department intubation of children when Broselow tape is unavailable.
Anesthesia resident and nursing education on pediatric airway sizing formulas.
PICU or NICU rapid reference for ETT size during respiratory failure.
Cross-checking a selected tube size against the Cole or Motoyama formula.
Estimating insertion depth at the lip to guide initial tube placement.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu