This paper presents four design charts (DC) to work as a simplified, easy-to-use and cost-effective tool to assist architects and building designers on sizing openings to deliver natural ventilation (NV) for cooling. The DC are derived from analytical techniques for four NV design systems based either on buoyancy-driven or wind-driven flow. The application of the DC is demonstrated to size NV openings for a bedroom in an apartment located in three Indian cities for two opening size scenarios: ‘business as usual’ (A); and ‘necessary size’ (B) to deliver the desired ventilation rates for cooling. The ventilation rates for cooling found with these DC are compared with outputs from computational fluid dynamics simulations. Findings show that for the earlier design stage the derived DC are effective tools. It is also found that the opening sizes used in scenario A do not deliver the desired NV rates for cooling, whilst the openings for scenario B must be sized separately for each city to be effective.