The adoption of the best available estimate for the stator Leakage reactance is the first step in several equivalent circuit of synchronous machine parameter estimation. However, there is no specific test for its direct measurement. This paper presents a simple and riskless procedure to estimate the Leakage reactance using the information obtained from the Constant Excitation Test. The method theory is described and is applied to several machines from laboratory to hydro power plants. In the absence of absolute values of the Leakage reactance, the estimates are compared to the Potier and sub-transient reactances.