Skin pressure is a biomechanical measure widely used in the assessment of load carriage systems. However, because of the complicated contour of human body, the stiffness of the pressure sensor array, and the large range of measurable pressures, there is much variability in previously reported results. In this paper, a simple mechanical model for load carriage was proposed, and the skin pressures beneath the shoulder and hip straps were predicted from the strap forces based on Laplace’s law. The proposed model was used to analyze data from literature with an aim to check the reliability of existing pressure measurements. The static and dynamic pressures at five locations on eight subjects wearing a backpack with a 10 kg load, while standing and walking on a treadmill, were measured respectively using pressure sensors of the air pack type. The combination of literature data analysis and experimental testing proved that the existing measurement method of interface pressure in load carriage systems often leads to over-estimation and this might misguide the pressure criteria set for load carriage system usage and design. The proposed model will be useful for quick prediction of the interface pressure in load carriage systems.