Analysis and prediction of the heights of sea waves in terms of a conventional crest-to-trough definition present practical and theoretical difficulties. As a closely related alternative, the envelope of waves can directly be used as a reference for a wave height measure that is continuous in time. This concept is explored to show that not only it is consistent with the theoretical specification of irregular waves but that it also provides a remarkably efficient approach for the frequency analysis of wave heights in typical applications. Theoretical arguments and a specific case study reveal that the proposed approach generates frequency estimates which are improved in statistical quality and compare better with the available theories on the distribution of wave heights.