This paper presents a new model for predicting the fluid flow through a Marsh funnel. Based on the Herschel-Bulkley fluid model, the model considers both the friction force and the dynamic force. Pressure drop due to the yield stress in the conical section is accounted in the model. In addition, an improved testing system is proposed for the validation of this new model. Experiments were conducted with several Newtonian fluids as well as some non-Newtonian fluids. Experiments and model results on dynamic forces show good agreement. Although the model slightly underpredicts the Marsh funnel time, the overall match is good. The general agreement suggests that the new model can be used for a fast estimation of the rheology parameters of a liquid using Marsh funnel test results and can be used in field applications.