International: pleural guidance agrees that ultrasound is essential to locate fluid, guide procedures and identify complexity, but there is no single universal formula for volume. Use the calculator as an estimate, and document patient position and measurement technique.
Measurements and reference values
Measurement
Usual value
Note
Pleural effusion — maximum interpleural separation
measure mm
Largest distance between parietal and visceral pleura in the largest free pocket; basis of the Balik formula in supine patients.no measurable fluid: <10 mmestimable, context-dependent: 10–30 mmlarge or symptomatic: >30 mm + clínicaSource: Balik 2006 / EFSUMB / ERS
Pleural effusion — craniocaudal height
measure cm
In sitting or upright patients, measure the vertical fluid extent along the lateral/dorsolateral chest wall.not measurable: 0 cmsmall to moderate: <10 cmlarge, correlate symptoms: ≥10 cmSource: Goecke / Ibitoye / Hassan
Lung base–diaphragm distance
measure cm
Subpulmonary distance used in Goecke 2 and Hassan formulas; improves the estimate when added to lateral height.Source: Goecke / Hassan / Ibitoye
B-lines
≥ 3 per space or field
Diffuse bilateral pattern favors interstitial edema; focal or asymmetric pattern favors pneumonia, contusion, atelectasis or fibrosis.few/isolated: 0–2interstitial syndrome: ≥3diffuse pattern with distress: clinical urgencySource: BLUE / ERS statement
Nodular pleural or diaphragmatic thickening
> 10 mm
When associated with pleural/diaphragmatic nodules or complex effusion, it is suspicious for malignancy; fluid should be analyzed when indicated.no thickening/nodule: absentsmooth/contextual thickening: <10 mmsuspicious: >10 mm ou nodularSource: EFSUMB chest ultrasound / pleural malignancy reviews
Classifications and calculators
Interactive calculator — pleural effusion
Method
How to measure
Formula / use
Balik — supine
Maximum pleural separation in millimeters, in the largest free pocket.
Estimated volume = 20 × separation in millimeters. Useful at bedside; meaningful average error, does not replace measured drainage.
Eibenberger — supine
Separation between lung and posterior chest wall in millimeters.
Estimated volume = 47.6 × separation − 837. May become negative for small volumes; use as comparison.
Goecke 1 — sitting
Craniocaudal effusion height in centimeters.
Estimated volume = height × 90. Simple, but less complete than adding the subpulmonary distance.
Goecke 2 / Hassan — sitting
Lateral height + distance between lung base and diaphragm, in centimeters.
Estimated volume = (height + distance) × 70. Good correlation in drainage studies, still an estimate.
Do not use formula alone
Septations, internal echoes, pleural nodules, trauma, fever or marked dyspnea.
Color should be driven by complexity and clinical context; large volume does not define etiology.
Document side, patient position, window used, measurement used by the formula, and whether the fluid is free or loculated.
Source: Balik 2006 / Ibitoye 2018 / Hassan 2017 / EFSUMB / ERS
Pleural effusion — ultrasound appearance and meaning
Appearance
Practical interpretation
Color
No measurable pleural fluid
Normal for the question “is there effusion?”; still assess sliding, lines and consolidations according to symptoms.
Green: consensus normal for effusion.
Anechoic, free, mobile
May be transudate or exudate; ultrasound does not establish etiology without clinical/laboratory context.
Yellow: abnormal but not necessarily complicated.
Complex non-septated
Echoes/debris may occur in exudate, older hemothorax, inflammation or malignancy; correlate.
Yellow: contextual zone.
Septated, loculated or thick debris
Suggests complicated effusion, organized empyema or hemothorax; drainage may be difficult and diagnostic aspiration is often relevant.
Red when infection, trauma, marked loculation or clinical worsening is present.
Pleural/diaphragmatic nodules or nodular thickening >10 mm
Suspicious for malignancy, especially with recurrent or unilateral effusion.