An indoor air quality (IAQ) metric that generally accounts for the effects on health and comfort of the total combination of gaseous contaminants is described herein. Acceptable concentrations of individual contaminants are taken to be the most stringent of several established exposure limits. Individual measured concentrations are compared with those limits to determine their individual relative acceptability. These relative ratings are then combined in an overall summation, or index, to provide a means to compare air quality in different samples containing differing gaseous contaminants with varying levels of individual contaminants. Thus this IAQ metric accounts for the relative effect of individual compounds on overall health and comfort as well as synergistic effects of low-level individual concentrations on the total air quality. Moreover, the metric clearly identifies those contaminants that have an adverse effect on air quality and should be remediated. Use of the metric is demonstrated in both airliner and building applications. Evaluation based on actual measurements provides a quantitative, comparative metric based on objective data. The airliner model and metric assessment includes a prediction of the impact of reducing the fresh air ventilation rate on overall air quality. It indicates that as the fresh air rate is reduced, air quality deteriorates if air purification is not provided. In order to improve the usefulness of this approach in evaluation of indoor air quality, further work in establishing individual acceptable concentrations of contaminants is suggested.