Reasonable quantification of space cooling load is helpful to utilize effectively the ventilation systems in a built environment. Studies have shown that the local cooling load (LCL) in a general non-uniform indoor environment is typically not equal to the heat gain. However, the quantitative relationship between heat gain and LCL is still unclear. Based on the analytical expression of non-uniform air temperature distribution, a quantitative relational expression between them is derived theoretically in this study. Experiments are conducted for validation, and six cases are designed for further demonstration. The results indicate that the LCL is equal to the sum of the products of the individual heat gain and its influence to local zone. The influence of one heat gain to local zone is described with the average accessibility of heat source (AAHS), and it can be less than, equal to or greater than 1. The air distribution system, heat sources distribution, and target zone have a big impact on the AAHS, which ranges from 0.40 to 1.67 in six cases. The established quantitative relationship between heat gain and LCL can provide theoretical guidance for designing air terminals and reducing the air-conditioning load in a general non-uniform indoor environment. (C) 2019 Elsevier Ltd. All rights reserved.