Heat transfer for fully developed flow between parallel plates has been investigated widely throughout literature. Results are given in form of either piecewise or continuos functions for the local and overall Nusselt-number. While the first type of correlation might be more accurate the latter is easier to use. On the other hand there is no sense in correlating local and overall Nusselt-number separately, as they are connected by definition. Therefore we derived a correlation for the overall Nusselt-number to the above named problem from the series solution of the temperature field, which is continuos and more accurate than any other correlation known to us. The corresponding local Nusselt-number is easily calculated from that correlation. The result is, too, better than from any other correlation known to the authors.