The conductance and sensor response of metal oxide chemiresistive gas sensors have a high dependence on ambient temperature and relative humidity. A simple mathematical model for calculating the dependence on ambient conditions for most of the commercially available metal oxide gas sensors is proposed. The model has an exponential relationship to ambient temperature and a linear relationship to relative humidity. Tin dioxide-based commercial metal oxide gas sensors, produced by Zhengzhou Winsen Electronics Technologies Co. Ltd., are considered for analysis. At various relative humidities, the sensor response is extracted from the sensor response vs temperature curves provided in the datasheets of commercial metal oxide gas sensors. Model parameters are evaluated from the extracted sensor response curves. The sensor responses calculated using the model are compared with those extracted from the datasheets. The model predicts the sensor response with a root mean square (RMS) error of less than 5%. We have also observed that the model with the same model parameter fits multiple sensors. The sensors are deployed at various locations on our campus for four months, along with electrochemical sensors having a higher sensitivity for comparison. The resistance in air measured using the sensors studied was within a limit of ±3% of its average after the correction of the effects of humidity and temperature.