We propose a simple method to evaluate the first and second magnetic anisotropy constants of high-density magnetic recording media with their easy axis in the film plane. By measuring the magnetization curve along the film normal, uniaxial anisotropy constants K1 and K2 can be determined simultaneously. The present method has been applied to (11·0) oriented CoCrPtTa hard disk media. The measured anisotropy constants are presented along with their temperature dependence. We also point out serious shortcomings of the currently used evaluation methods, such as the rotational hysteresis method and the singular point detection technique, which usually overestimate the magnetic anisotropy constant.