Cemeteries are supportive parts of the urban green ecosystem due to cooling services that improve urban microclimate. This study aims to provide a quantitative understanding of internal-external cooling effects of cemeteries in Istanbul, high-density metropolitan area suffering from overheating and lack of greenspaces. There are 309 ‘cemeteries’ of diverse shapes and sizes in Istanbul's urban landscape, covered by green elements, impervious surfaces, and water bodies. We conducted a six-stage methodology: sampling design including a taxonomy of patches in super-small/small/medium/large classes; calculation of land surface temperature (LST); determination of cool island intensity and cooling extent; measurements of landscape metrics; Ridge Regression Model iterations; and buffer distance sensitivity analyses in cooling gradients. The research found that cemeteries have remarkable cooling potential, with internal LST between 1.5 and 3 °C below LSTurbanaverage. Cooling efficiency was sensitive to patch size and the building density around the green patches. Even though the influence of patch size on the cooling efficiency was stronger than the landscape patterns, the bigger was not always the better in regulating the thermal environment. Planning super-small/small green patches in high-density centres is a more practical and efficient way to regulate urban neighbourhoods in Istanbul. The study helps professionals for heat mitigation and thermal regulation in the urban environment through green space planning.