Ion mobility spectrometry (IMS) is widely used to characterize compounds of interest (COIs) based on their reduced mobility ( K0) values. In an attempt to increase the accuracy and agreement of studies, the most recommended method has been to use a reference compound with a known K0 value to calibrate the instrument and calculate COI K0 values from normalized spectra. Researchers are limited by the accuracy of previous K0 value reference measurements on which to base their calibrations. Any inaccuracy in these reference K0 values, typically ±2%, will propagate through to the calculated K0 value of the COI. For this reason, there is a need to standardize reference K0 values with improved accuracy. Through improvement of the accuracy of reference measurements, a lower degree of error will propagate through new K0 value calculations. The K0 values of the ammonium reactant ion, the potential reference standard dimethyl methylphosphonate (DMMP), and three explosive COIs were characterized at multiple drift gas temperatures, drift gas water contents, and electric field strengths on an accurate ion mobility spectrometry instrument. K0 values reported here are known to ±0.1% as a result of reducing the error of all instrumental parameters.