What is the normal diameter of the main bronchi?

Normal Main Bronchi Diameter

The normal diameter of the left main bronchus ranges from 10-12 mm in adults, with men averaging 12.4 mm (range 9.5-15.5 mm) and women averaging 10.7 mm (range 9.0-14.0 mm). 1

Anatomical Measurements

Left Main Bronchus

• Adult males: Mean diameter of 12.4 ± 1.5 mm, with a range of 9.5 to 15.5 mm 1
• Adult females: Mean diameter of 10.7 ± 1.0 mm, with a range of 9.0 to 14.0 mm 1
• The left main bronchus is approximately 5 cm in length 2
• Diameter measurements are typically taken at 2 cm below the carina for standardization 3

Right Main Bronchus

• The right main bronchus has a mean length of only 1.09 cm (range 0 to 2.9 cm) from the carina to the origin of the right upper lobe bronchus 2
• This is significantly shorter than the commonly cited 2.0-5.0 cm found in many anatomy textbooks, which is incorrect 2
• The right main bronchus is wider and shorter than the left, though specific diameter measurements are less commonly reported in the literature

Predictive Relationships

Size Correlations in Males

• In male patients, bronchial diameter correlates with age and height: diameter (mm) = 0.032 × age (years) + 0.072 × height (cm) - 2.043 1
• For a 50-year-old male who is 172 cm tall, the predicted left bronchial diameter is approximately 12.0 mm 1

Size Correlations in Females

• In female patients, no significant correlation exists between bronchial diameter and age, height, weight, or body surface area 1

Tracheal-to-Bronchial Ratio

• The left bronchial width to tracheal width ratio is consistent across sexes: 0.75 ± 0.09 in men and 0.77 ± 0.10 in women 4
• This ratio can be used to predict left bronchial diameter when tracheal width is known but direct bronchial measurement is unavailable 4

Clinical Imaging Context

CT Assessment Standards

• The American Thoracic Society/European Respiratory Society recommends that airway diameter measurements be made in 2D slices perpendicular to the centerline of the airway segment 5
• Physical measurements including diameter, cross-sectional area, and luminal perimeter should be obtained from the original gray-level CT volume 5
• Modern multidetector CT can reconstruct the first 6 to 10 bronchial generations with measurements that agree well with anatomical casts 5

Pathological Thresholds

• A segmental pulmonary artery to accompanying bronchus ratio >1:1 suggests pulmonary hypertension 5
• Bronchial artery enlargement to a diameter >1.5 mm can be seen in patients with pulmonary hypertension 5

Important Clinical Caveats

• Measurement technique matters significantly: 3D CT reconstructions show only moderate correlation with 2D measurements for bronchial dimensions, and same-sized double-lumen tube predictions matched in only 69% of men and 34% of women when comparing methods 3
• Posteroanterior chest X-ray measurements require correction for magnification of intrathoracic structures, with potential distortion up to 5% 2
• The right main bronchus length is highly variable (0-2.9 cm), making anatomical landmarks critical for procedures 2