From heat balance measurements in the ablation area of West Greenland (EGIG-profile, 1,013 m a.s.l., 69°40'N, 49°38'W) the positive-degree-days-factor is interpreted by the heat balance characteristics. The positive-degree-days-factor depends on the heat transfer coefficient and is a function of the share of the sensible heat flux density to the heat of melt. Using simple approximations the calculated positive-degree-days-factor is in good agreement with the measured value.