At what depth (distance from the teeth) should a 7.0 mm endotracheal tube be positioned in an adult male of average height (170 cm)?

Endotracheal Tube Depth in Adults

Standard Depth Guidelines for Adult Males

For an adult male of average height (~170 cm), the standard recommended ETT depth at the incisors is 23–25 cm. This is the widely accepted clinical guideline taught in Miller's Anesthesia and endorsed by the ASA/difficult airway guidelines.

The "Size × 3" Formula — Limitations

The commonly cited formula Depth (cm) = ETT size (mm) × 3 gives:

However, this formula is a rough approximation and underestimates the correct depth for average adult males. The formula is more applicable to pediatric patients and smaller adults. For a standard adult male, the tube tip should sit approximately 4–5 cm above the carina, which corresponds to a depth of 23–25 cm at the teeth.

Depth Guidelines by Patient Group

Reference: Miller's Anesthesia, 8th edition; Morgan & Mikhail's Clinical Anesthesiology — standard adult male ETT depth is 23–25 cm at the incisors.