Accurate quantification of pleural fluid is important. USG (ultrasound) is a non-invasive method, but measurements and calculations have not been standardized. Consecutive patients planned for thoracoscopy were recruited just prior. USG examination was performed by 2 independent observers to obtain measurements (Fig.1) leading to 5 calculations: 1. EV(Estimated Volume) = X(Craniocaudal extent of the effusion at the dorsolateral chest wall) x 90, 2. EV = X + LDD (Lung base to mid-diaphragm distance) x 70, 3. EV= 47.6 x A (Maximum perpendicular distance between the pulmonary surface and chest wall at maximal inspiration) ? 837, 4. EV = 20 x A and 5. EV = 16 x Parietal to Visceral pleura distance at the level  of mid-diaphragm. The amount of pleural fluid drained was accurately measured.57 patients were recruited.By Pearson?s correlation, the estimated volume from each calculation was compared with the amount of fluid drained.All 5 methods of USG had significant (p<0.001) but modest correlation with the amount of fluid drained with ?r? values of 0.645, 0.616, 0.598, 0.603 and 0.646 respectively.The intraclass coefficient between the 2 observers for all methods were 0.949 (95%CI 0.914,0.97). Modified Bland Altman Plot (Fig.2) revealed that methods 1 (Erect- craniocaudal extent of effusion) and 5 (Supine-parietal to visceral pleural distance) were more reliable, particularly when the volume of the fluid was 900-2200ml and 1200-2200ml respectively.In all methods there was inaccuracy above 3000ml. To conclude, our study demonstrates that the estimated volume through USG is reliable in the quantification of pleural fluid particularly when the fluid is of moderate quantity.