To calculate the load capacity of a steel prop, you need to consider several factors. First, determine the allowable stress for the steel prop material. Then, measure the dimensions of the prop, including its length, diameter, and thickness. Next, calculate the cross-sectional area of the prop. Multiply this area by the allowable stress to obtain the maximum load capacity. Additionally, take into account any additional factors like safety margins, environmental conditions, and the type of load being supported to ensure accurate calculations.