Coke oven batteries utilize stamp charged coal cakes for production of high quality blast furnace coke. Crushed coal blends are mechanically stamped to produce coal cakes. It is crucial to have a good control over this stamping operation so as to achieve a uniform bulk density (approximate to 1100-1200 kg.m(-3) wet basis) of coal cake post stamping. This can facilitate robust and energy efficient coking operation. The dynamic nature of the stamping operation necessitates an online bulk density measurement technique. An ultrasonic technique which enables online measurement of bulk density during the stamping operation is described. The ultrasonic response was found to have a straight line correlation with bulk density (wet basis) and moisture content of stamped coal with an R-2 value of 0.98. The effect of moisture content in the coal on the ultrasonic measurements is also discussed. A lab scale prototype was developed with integrated sensors to emulate online measurement. The prototype was found to have a measurement error of less than +/- 1.6%. This method can also be suitably adapted for online bulk density measurement of granular solids other than crushed coal.