Soil gas sampling has been used for decades in environmental site assessment and monitoring programs, with the results used to focus subsequent, more invasive and expensive sampling and remediation (i.e., soil and groundwater), evaluate the performance of a remediation system, or identify new contaminant releases. More recently, soil gas sampling has become the standard approach in evaluating the potential for the intrusion of gas-phase volatile and semi-volatile compounds into confined structures and spaces in concentrations high enough to pose a human health risk to the occupants therein. Conventional soil gas sampling utilizes active or passive methods. Active methods force an extraction of soil gas from the subsurface environment at a point in time or over a relatively short time period. Passive methods rely on natural, concentration-gradient-driven diffusion of compounds in the gas-phase through the soil pore space to the sampler for continuous collection. Passive methods are generally simpler to use in the field and allow for sampling under a wider range of site conditions, with less data variability, than active methods. Data from passive soil gas sampling often are considered semi-quantitative (measured mass/compound/sampler) rather than quantitative (measured mass/measured volume) when compared with active methods. However, with careful measurement of the sampling rate, and accounting for the resistance to gas diffusion in the soil environment, soil gas concentrations can be reported using a sorbent-based passive sampler. This paper discusses the calculation of vapor concentrations for the AGI Universal Sampler (formerly known as the GORE Module) using the sampler's measured uptake rate, time of exposure, and sorbed contaminant mass. Additionally, this paper presents example data demonstrating that passive sampling techniques can deliver quantitative data.