RATIONALE: Collisional cross sections (CCS) are an important characteristic of gas-phase ions that are measured using ion mobility-mass spectrometry (IMS). Typically, CCS measurements are performed with drift-tube IMS or travelling-wave IMS. However. in a high-field asymmetric waveform ion mobility (FAIMS) device, the non-linear path through the device makes CCS determination more challenging. This research explores whether CCS can be predicted using a microscale FAIMS by using known CCS standards. METHODS: An Owlstone ultraFAIMS microscale FAIMS spectrometer was coupled to an Orbitrap Exactive mass spectrometer. 2 different CCS standard mixtures (tetraalkylammonium halides and poly-DL-alanine oligomers) were used to evaluate the systems potential to predict CCS. Test peptides bradykinin acetate and substance P were used to determine prediction accuracy for singly and doubly charged peptide species using external calibration with a series of poly-DL-alanine peptides for +1, +2 charge states. RESULTS: Calibrations with excellent correlation coefficients (R 2 = 0.99) for both TAAHs and poly-DL-alanine were obtained. Good predictive accuracy was achieved for bradykinin [M+2H] 2+ with a ±0.5% difference between experimental and published CCS at a dispersion field strength (DF) of 250 Td, the model proved less accurate for bradykinin [M+H] + (±1.4% at 240 Td). The prediction accuracy for the [M+H] + and [M+2H] 2+ ions of substance P was within ±5% and ±3% at 250 Td respectively, while at higher DF values accuracy decreased to approximately 5%. CONCLUSIONS: Distinct relationships were observed between CCS and transmission CF with both calibrants. Optimum predictive performance was obtained at DF strengths of 240-260 Td. At lower DF accuracy is reduced by insufficient resolution of analyte ions from solvent cluster adducts while at higher DF values, poor transmission becomes a factor. Nevertheless, these data suggest microscale FAIMS can conduct CCS measurements with reasonable accuracy when the compound being measured has similar structural features to the CCS standards used.