A new technique has been developed to determine the sintering rate of coal ash based on the measurement of the pressure-drop across a pellet of ash. The technique monitors the changes in porosity as a function of time, which is an indication of the degree of strength development due to sintering. The technique developed in this study shows a good repeatability of the rate of sintering and confirms that viscous flow is the dominant mechanism for sintering of coal ash. The activation energies of the sintering process studied in this investigation were found to be in the range of 200−315 kJ/mol.