Abstract: The volume of the blast furnace hearth deadman directly restricts the flow channels of slag and hot metal as well as the effective hearth volume, serving as a critical factor for blast furnace stable operation and long-term campaign life. Existing studies have extensively investigated the morphology and behavioral characteristics of the hearth deadman, yet the quantitative characterization of its volume remains insufficient. Based on the macroscopic morphological features of the deadman revealed by the dissection of a blowndown blast furnace, this paper proposes to geometrically equate the hearth deadman to a combined solid consisting of an upright frustum and an inverted frustum, and establishes an equivalent volume calculation model for the hearth deadman determined jointly by design parameters, directly adjustable parameters, hearth state response parameters and boundary equivalent parameters. A 2 580 m³ blast furnace was taken as the research object. This study determined the selection principles of model parameters and calculated the equivalent volume of the deadman. The influence laws of multiple factors including taphole depth, taphole angle, blast velocity, distance from the front end of the raceway to the deadman edge, vertical distance from the deadman corner to the center line of the taphole, and inclination angle of the inverted frustum were analyzed. The results show that the maximum cross-sectional radius at the deadman corner of the blast furnace is 3.826 m, accounting for 74.81% of the hearth radius. The equivalent volume of the deadman is 239.3 m³, occupying 43.50% of the total hearth volume, and the volume of the upper upright frustum accounts for 92.08% of the total deadman volume. Among all the influencing factors, taphole depth exhibits the most significant influence on the deadman volume, followed by the distance from the front end of the raceway to the deadman edge and blast velocity. The vertical distance from the deadman corner to the center line of the taphole increases the deadman volume positively, while the taphole angle and the inclination angle of the inverted frustum have relatively weak effects. The research results confirm that the proposed model can quantitatively characterize the spatial occupation degree of the hearth deadman. It can provide a quantitative reference for hearth state diagnosis, optimization of taphole maintenance systems, adjustment of air supply systems and long-life control of blast furnace hearths.