There is growing evidence of the high transmission potential of COVID-19 through virus-laden aerosols. Because aerosols are inhaled in various concentrations, an overall assessment of transmission risks at different indoor scales is crucial. However, a comprehensive risk assessment method that evaluates the direct link between short-range and room-scale zones is still lacking. In this paper, a risk assessment model combining both short-range and room-scale effects is developed to obtain effective reproduction number in confined indoor environments, called Turbulent Jet Wells Riley (TJWR) model. Combined with the viral load data and aerosol generation data of different human respiratory activities, the Monte Carlo simulation method is applied to calculate the quanta emission rate, which further provides the input parameters of the TJWR model. Three known outbreaks (Hangzhou banquet hall X, Guangzhou restaurant Y, and Hong Kong restaurant Z, China) are chosen to validate the TJWR model. Results show that the TJWR model is more efficient than the original Wells-Riley model. The average relative error of the TJWR model ranges between 9% and 44%, while for the Wells-Riley model, it ranges between 57% and 78%. The TJWR model also proves that infection risk assessments using the well-mixed assumption can systematically underestimate the transmission risk for those close to the source. Additionally, there is a significant positive linear correlation between the total number of exposed individuals at the short-range and the effective reproduction number. This newly developed TJWR model has great potential for rapid and real-time overall airborne transmission risk assessment in buildings and cities.