Pneumothorax Size Estimator
Use chest X-ray measurements to estimate pneumothorax size. Choose a method, enter values in centimeters, and click calculate.
Educational use only. This tool does not diagnose or replace urgent clinical assessment.
What this pneumothorax calculator does
A pneumothorax is air in the pleural space that can partially or completely collapse a lung. One common question after seeing a chest X-ray is: how large is it? This calculator estimates pneumothorax size as a percentage using standard radiographic formulas.
Size estimates can help structure clinical communication, support documentation, and track change over time. They should always be interpreted alongside symptoms, oxygenation, hemodynamics, and imaging quality.
Methods included in this calculator
1) Collins method
The Collins equation uses three interpleural distances measured on chest radiograph:
- A at the apex
- B at mid-lung
- C at lower-lung level
Formula: % Pneumothorax = 4.2 + 4.7 × (A + B + C)
2) Light index
The Light index approximates volume loss using the ratio between collapsed lung diameter and hemithorax diameter.
Formula: % Pneumothorax = 100 × [1 − (d/D)3]
- d = collapsed lung diameter
- D = hemithorax diameter
How to measure correctly on chest X-ray
- Use a clearly visible pleural line.
- Measure in centimeters and keep consistent magnification.
- Avoid mixing AP and PA films for serial comparison when possible.
- If landmarks are unclear, use CT or expert radiology review for precision.
How to interpret the estimated percentage
The calculator reports an estimated size category:
- Small: < 20%
- Moderate: 20% to 40%
- Large: > 40%
These categories are practical labels, not definitive treatment rules. Clinical condition remains the key driver of management.
Important clinical context
A seemingly small pneumothorax can still be dangerous in the wrong setting. Immediate medical assessment is crucial if there are signs such as:
- Severe breathlessness or rapidly worsening chest pain
- Hypotension, tachycardia, or hypoxia
- Possible tension physiology
- Trauma, mechanical ventilation, or significant underlying lung disease
Limitations of calculator-based estimates
- 2D X-ray measurements estimate a 3D problem.
- Positioning and rotation can change apparent distances.
- Different formulas may give different percentages in the same patient.
- Management decisions depend on much more than size alone.
Bottom line
This pneumothorax calculator is a fast, practical way to estimate size from radiographic measurements. Use it to support clinical thinking, not replace it. If a patient may be unstable, treat the situation as urgent and follow institutional emergency protocols.