The working group WG4 of ISO TC 205 aims to define Indoor Air Quality criteria. The draftstandard contains several methods for determining ventilation rates, based on these criteria.The ventilation rates obtained with some of these methods are compared for several premises:ASHRAE 62-1999, the method of perceived IAQ of CR 1752, and the prescriptive method ofAS 1668.2. To improve the comparison, ventilation rates are also calculated with the prEN13779 method.The studied buildings contains offices, classrooms and a play area. Ventilation rates obtainedwith real occupancy and default occupancy given in the draft are also compared. Then, theway to take into account smokers by the different methods has also been considered.There are large discrepancies in the results: the CR 1752 category A always gives the highestventilation rates, while the ASHRAE version in the ISO TC 205 and AS 1668 often givelowest results. Use of default occupancy increases the differences.