With the aid of aluminum oxide reference films, analytical techniques that previously provided only relative thickness information can now report absolute mass thickness measurements for aluminum oxide films. These new reference films were dense, nonporous, anodic aluminum oxide films grown by the method of Haas with a thickness range from 12 to 135 nm. Dimensional thickness measurements were made by transmission electron microscopy and spectroscopic ellipsometry. Absolute mass thickness measurements were made by electron probe microanalysis and energy-dispersive x-ray microanalysis. Relative thickness measurements were made by infrared spectroscopy, x-ray photoelectron spectroscopy depth profiling, and wavelength-dispersive x-ray fluorescence spectroscopy. Characterization measurements show the growth recipe (1.35 nm/V) predicts the dimensional thickness within 5%-10% and the mass thickness within 10%. Little or no evidence of hydration or phase change is observed after five years storage. Numerous surface-processing procedures involving aluminum material, such as brazing, welding, wetting, bonding, stamping, and rolling, will benefit from improved measurements of oxide-layer thicknesses on aluminum or aluminum alloys.