In this paper an analytical solution to the diffraction of elastic waves by penny‐shaped cracks in metals is compared with experimental observations. The analysis, which is based on elastodynamic ray theory, is valid for the region of ka ≳ 1. A digitized spectrum analysis system is described which measures the frequency components of the waves diffracted from a 2500‐μ‐radius crack in diffusion bonded titanium. The amplitude spectra show good agreement between experiment and theory. The theoretically predicted periodicity of the diffracted spectra provides a simple formula for the inverse problem. Application of this formula to the experimental measurements determines the crack size with excellent accuracy.