Three different calibration techniques have been developed to greatly improve the accuracy of the solid holdup distributions obtained from electrical capacitance tomography (ECT) measurements. First, liquid mixtures are used to calibrate the ECT system. Second, the relative permittivity of solid particles is obtained by immersing the solids in different fluids: the solid relative permittivity corresponds to the point where the fluid relative permittivity matches the relative permittivity of the liquid-solid mixture. Third, the best relationship between solid holdup and electrical permittivity, over the required range of solid concentrations, is determined, for each particulate system, by suspending the particles in a viscous liquid honey.Three different calibration techniques have been developed to greatly improve the accuracy of the solid holdup distributions obtained from electrical capacitance tomography (ECT) measurements. First, liquid mixtures are used to calibrate the ECT system. Second, the relative permittivity of solid particles is obtained by immersing the solids in different fluids: the solid relative permittivity corresponds to the point where the fluid relative permittivity matches the relative permittivity of the liquid-solid mixture. Third, the best relationship between solid holdup and electrical permittivity, over the required range of solid concentrations, is determined, for each particulate system, by suspending the particles in a viscous liquid honey.