Objective To study the method of calculating the designed hopper rated capacity of ton bag packing machine when designing its hopper. Methods By analyzing and simplifying the work process of the packaging machine and the change trend of granular materials in the hopper during the whole working cycle, the requirements to be fulfilled by the hopper and the maximum amount of material in the hopper were studied, and the hopper rated capacity was designed based on the maximum amount of material in the hopper. Results The maximum amount of material in the hopper depended on the feeding rate, the nesting rate and the packaging specifications,and there were clear relationships among them. Therefore, the maximum amount of material in the hopper could be calculated based on the known parameters such as feeding rate, nesting rate and packaging specifications. Conclusion Under the prerequisite of ensuring the continuous and stable nesting of the hopper and avoiding overflow, a method was proposed for the calculation of designing hopper rated capacity, through which the designed rated capacity for the hopper of packing machine could be calculated.