Accurately and easily quantifying the greenspace cool island intensity (GCII) is important to understand the cooling effect of urban greenspace for better urban greenspace planning and management. This study proposed two new methods (i.e., equal area method and equal radius method) to estimate GCII and compared them with two old methods (i.e., turning point method and fixed radius method) in terms of the GCII magnitudes, spatial variations, relationships with greenspace size, and the estimation of optimal greenspace size in cooling the environment (i.e., threshold value of efficiency (TVoE)). We performed the analysis based on Landsat derived land surface temperature (LST) in seven Chinese cities with varied climate background and geographic variations. The results showed that: (1) Different methods significantly impacted the estimated GCIIs with higher values by the turning point method and lower values by the equal area method. (2) GCIIs by different methods were positively and significantly correlated with each other and characterized similar spatial heterogeneities. (3) GCIIs by all methods showed significantly positive logarithmic relationships with greenspace area with higher R2 observed by the equal area method. (4) The four methods estimated close TVoEs with no significant difference among them. We recommend the equal radius method to quantify GCII for its equal effectiveness but easier calculation compared to other methods.