Knowledge of the absolute, versus relative, performance characteristics of VHF and UHF radars used in geophysical applications is often important. We suggest that the Moon may form a convenient, easily tracked calibration target for many such radars. The lunar absolute radar scattering crosssection is large, reasonably well known (∼7% of the visible disk) and is essentially wavelength independent over 6 m>λ>1 cm. The Arecibo 430‐MHz radar system was calibrated using the Moon as the target. These measurements, which are discussed in detail, yielded cross sections of 4.0% and 4.6% for a special 6 W and the main 1.6‐MW transmitters, respectively. We develop and present the radar equation appropriate to all total power calibration procedures including the Arecibo “worst case” calibration. We also discuss error levels, the necessity for averaging to obtain valid cross sections, and other practical difficulties associated with the