This paper presents a new estimation method for the equivalent thermal conductivities of the compact slot windings formed from round conductors. The estimation accuracy of thermal conductivities is essential for peak temperature prediction to avoid overheating failures in the high power density electromagnetic devices. The compact windings with orderly wound conductors perform better on heat dissipation and take smaller slot space than the random wound types. In recent years, the winding technology has made great improvement, and the compactness of conductors is significantly elevated. After observing the cross section of the windings, the randomness of the wire's layout is greatly reduced and a certain regularity is shown. The proposed estimation method takes the geometric characteristics of the internal structure into account to improve the estimation accuracy of the traditional methods, which use the proportion of each material only. Considering the layout of conductors is not completely regular, the impact of the dislocation between conductors is explored. Then, the conclusion is used to modify the analytical result. The experimental test result shows that the proposed theoretical method is easy to apply and meanwhile performs satisfactory in terms of high accuracy and low computation.