A rain parameter diagram is presented which displays the relationships between all rainfall parameters defined in terms of an exponential drop size distribution. Special emphasis is given to remotely measurable quantities such as radar reflectivity, microwave attenuation, and optical extinction. Although an exponential distribution is used to construct the diagram, it is shown to have general application for arbitrary size distributions and for a wide variety of rainfall-related problems. Some of the problems are (1) analysis of the sources of error which result from the use of empirical rainfall relations, (2) depiction of the physical differences between different types of rainfall and of the similarity between all empirical relations which apply to the same type of rainfall, and (3) determination of the accuracy with which remote measurements must be made to obtain accurate measurements of rain parameters. A set of overlays is shown for four common radar wavelengths and four temperatures which display the relationships between microwave attenuation and the other rainfall parameters. Methods are discussed by which these diagrams can be used to determine rainfall parameters remotely in dual-measurement techniques. The diagrams can also be used to find the errors in these rainfall parameters which result from errors in the two quantities involved in the dual-measurement technique.