Methods and apparatus to calibrate rod pump controllers are described. An example method includes obtaining initial values related to a pumping unit, determining parameters based on the initial values, the parameters including at least one of a leaked off load value, a residual friction value, and a buoyant rod weight value, and based on one or more of the initial values and the parameters, calculating one or more dimensions of a rod string, the one or more dimensions to be used to determine a pump card of the pumping unit.