The successful screening of insecticides, acaricides, herbicides, fungicides, ovicides, nematicides, growth retardants, and other biocidal compounds depends upon both the accurate preparation of test concentrations and the manner in which they are applied to the soil, host plant, or specific life stage of the organism. This preparation of test sprays, dips, dusts, and other formulations of test materials depends on the accurate computation of the equivalents used. The purpose of this manual is to provide a useful reference for entomologists and others in related disciplines who must prepare materials for screening in the laboratory, greenhouse, or small field plot. The effort was begun when it became apparent to the author that a single reference source in the form of a manual was not available. Further, many different procedures exist for calculating and expressing concentrations, including "rules of thumb," Pierson square, and others; these may be understood by some but not by all. The fact that the information gathered for this manual has come from a great many sources further emphasizes the variety of procedures in use and demonstrates the need for a reference of this nature.