There exist methods for computation of a focus that require a computer. These are based on ray acoustics in a horizontally stratified atmosphere. However, often a quick judgment must be made relative to the focal area of a high‐intensity sound source, and quick estimates are desirable. It is then adequate to determine the existence of a focus and its approximate location. The algorithm discussed here results in a simple technique for predictivg the existence and location of a focus for a common type of effective sound‐velocity profile.