A system, and computer usable program product for thermal relationships based workload planning in a data processing environment are provided in the illustrative embodiments. For a data processing system having a cooling correspondence with a cooling unit in the data processing environment, a determination is made of a fraction of an additional heat generation potential of the data processing system that the cooling unit will have to dissipate. Using the fraction and a cooling capacity utilization of the cooling unit at a given time, an expected cooling capacity utilization is computed. A workload on the data processing system is adjusted in response to the expected cooling capacity utilization exceeding a threshold.