Relating the empirical slump test to yield stress facilitates the capture of fresh state concrete performance in fundamental quantitative terms whilst avoiding the requirement for expensive rheological equipment. This paper proposes a novel method to predict yield stress from slump by directly measuring the height of the unyielded region via a 3D reconstruction approach. The efficacy of the proposed method is assessed through an experimental series of 21 tests. The results indicate a better correlation between the height of the unyielded region and yield stress compared to total slump height and yield stress. The proposed 3D reconstruction methodology predicts yield stress with significantly increased accuracy, indicated by a mean prediction error an order of magnitude lower than the average performance of existing models. The results of this study suggest that, for the first time, a valuable fundamental rheological property can be confidently derived from a standard concrete slump test.