Equations of ‘ventilation index’ in industrial and medical sectors are already established, but not yet been worked out for domestic household environments. This study intended to establish an empirical formula for ‘ventilation index’ for domestic indoor environments. Measurements of 2.5 micron size particulate matter (PM2.5) with biomass, air velocity, room index, temperature and relative humidity were used for developing the empirical formula. A total of 54 households from rural Andhra Pradesh and Karnataka states of India were selected.  Average air velocity ranges in selected kitchens were categorised into three parts for developing ventilation indices in household kitchen environments. Observations in kitchen environments were found to be very interesting and promising. The formula captured inverse relation between PM2.5 and air velocities, consistently.