Infiltration is the uncontrolled flow of air into the building through the envelope, which contributes to a significant amount of heat loss and is estimated to be around 30% of the heating demand. It is therefore essential to estimate the amount of infiltration, to design a suitable heating and cooling system in a building. Empirical relations which are used to determine infiltration, generally overestimate the infiltration rate, since the effects of weather, mechanical ventilation and building geometry are not taken into account. Large Eddy Simulation (LES) is used to determine the pressure distribution around a building along with an airflow network model to determine the infiltration flow rate. Validation studies of the LES model show that the pressure data at the front and back faces of a surface-mounted cube are accurately captured, whereas, the pressure at the top and side faces slightly deviate from reference data with an error of 16%-20%. This occurs due to a shift in the recirculation region at the top towards the leeward part of the cube surface. The reattachment of the flow is not observed at the top and side surfaces, which explains the deviations in pressure. The infiltration rate is analysed in the Matrix VII building using the in-house model, which combines the LES model and the airflow network model. It is then compared with other relevant standards and models like the NTA 8800 and an energy balance model. The comparison is made in terms of the cross-correlation between the models and the heat loss associated with infiltration. The in-house model shows good cross-correlation with the NTA 8800 model, with a Pearson correlation coefficient of 0.8454. The building standards which employ empirical relations, overestimate the heat loss by a factor of 10 compared to the in-house model. The in-house model is then used to develop a database of infiltration values for different building heights and airtightness values. The specific infiltration rate is observed to decrease in buildings taller than 120 m due to the minimal changes in velocity higher up the atmospheric boundary layer. The database is observed to provide values of infiltration with reasonable accuracy, compared to the existing database in the ISSO standard.