Room‐temperature optical absorption over a large dynamic range is reported for single‐ crystal undoped yttrium aluminum garnet (Y3Al5O12or YAG). Absorption results are presented for the energy ranges 1.8 to 3.0 and 4.5 to 6.5 eV. For this work, ultraviolet (UV) absorption measurements were performed on four different boules of Czochralski‐grown undoped YAG. Absorption features were observed at 4.8 and 5.6 eV which can be attributed, at least in part, to trace impurity concentrations. Along with the UV measurements, calorimetric absorption results are presented at several laser wavelengths in the visible and near infrared (IR). The calorimetric results suggest a value of 1.5×10−3cm−1for the absorption coefficient of undoped YAG in the red and near IR. From the combination of UV and calorimetric measurements, an empirical estimate of the absorption coefficient from the visible to the UV is presented for undoped YAG. In addition to the absorption spectra, detailed chemical analyses and sample histories are given for the as‐grown optical quality YAG utilized herein.