The mass and heat balances in circulating fluidized bed systems strongly depend on the overall solids flux recirculated, making it necessary to estimate or measure this flux. Many methods have been reported in literature to continuously monitor the solids flux, with the curve solids flux G(s) vs. pressure drop in the riser Delta P-riser riser as one of the most used approaches. In this work, we show that in a circulating fluidized bed equipped with an inclined standpipe the whole mass flux is well correlated with the standard deviation of the pressure fluctuations in the standpipe. Contrary to the correlation G(s) vs. Delta P-riser, our correlation results to be virtually independent of the superficial gas velocity in the riser in the range 3.1-7.5 m/s. This makes it applicable for the on-line monitoring of the solids flux in a broad range of superficial gas velocities. Moreover, it has been shown that from the data G(s) vs. standard deviation it is possible to estimate the maximum solids flux achievable by the unit. From this information, we can know at which fraction of the maximum mass flux the circulating fluidized bed is operating. (C) 2012 Elsevier B.V. All rights reserved.