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The capacity factor is an essential indicator in evaluating a wind turbine's efficiency. In this paper, four kinds of power curve models--linear, quadratic, cubic, and general--are applied to estimate the capacity factor of a pitch-controlled wind turbine based on the Weibull probability distribution of wind speed. The general model is adopted for the first time in this issue. The wire-frame graph of capacity factor is demonstrated for practical Weibull shape and scale parameters representing various wind farms. To analyze the validity of the four empirical models, seven power output curves provided by different manufacturers are selected for different operating speeds. The results show that a turbine generator installed at a wind site with larger scale and shape parameters may show greater performance, but limitations do exist. The capacity factors calculated from manufacturer data are far greater than those from empirical models if the cut-in, rated, and furling speeds of a wind turbine are set as 4, 15, and 25 m/s, respectively. Similar values from empirical models get closer to those from manufacturer data when the cut-in or rated speeds decrease. The quadratic model shows better agreement with manufacturers' power curves. [ABSTRACT FROM AUTHOR]