Monitoring volatile organic compounds is critical to mitigate the risks they pose to human health and the environment. Developing technologies for detection of VOCs requires methods to produce the desired concentrations for benchmarking. Herein, we present a simple, inexpensive, and flexible platform capable of producing user-specified concentrations of a gas-phase analyte for the purpose of fine-tuning and benchmarking VOC detection technologies. This technology, the gas-phase dilution apparatus (GPDA), is built around two mass flow controllers that mix precise flows of the analyte and dilution gas. We used a custom APPI-MS configuration as well as a commercial photoionization detector to detect benzene and toluene. These two detection methods were employed to assess the linear output of concentrations over a combined range of 1–20 000 ppbV which yielded average R2 values of 0.9980 and 0.9988 for benzene and toluene, respectively. Additionally, output stability was assessed at 10 ppbV, 1 ppmV, and 5 ppmV of benzene and toluene. Six measurements were averaged over the course of 30 min, and RSDs were below 2% for all three concentrations of both compounds. These results suggest that GPDA is capable of producing precise and repeatable concentrations of gas-phase analytes.