Low-frequency arrays (120--400 MHz) can be calibrated using a sky model based on sky maps. For a single antenna the variation of measured power with the Earth's rotation is needed to separate receiver gain and noise temperature. For an array an instantaneous calibration can be made using normalized correlations or normalized beam power for which the receiver gain cancels out. Examples of the sky model for various antenna orientations are shown along with measured data used to perform a calibration. The effects of unmodeled mutual coupling of the received signals and receiver noise on the calibration method are analyzed and are found to result in errors of only a few percent in an array of 5 ¿ 5 crossed dipoles designed to observe the deuterium line at 327 MHz.