This form returns the photometric transformation coefficients between Johnson-Cousins UBVI filters and WFC3-UVIS wide-band filters for a given object spectrum, as tabulated by Sahu, Deustua, and Sabbi (2014). The coefficients as given are the difference between the magnitude of the object in the selected Johnson-Cousins filter and the corresponding WFC3-UVIS filter. If you find that the options available here do not meet your needs, section 4 of the report describes a recipe for calculating photometric transformation coefficients using the Synphot task 'calcphot'.