  The Nancy Grace Roman Space Telescope's (Roman) Coronagraph Instrument is a
technology demonstration equipped to achieve flux contrast levels of up to
10$^{-9}$. This precision depends upon the quality of observations and their
resultant on-sky corrections via an absolute flux calibration (AFC). Our plan
utilizes 10 dim and 4 bright standard photometric calibrator stars from Hubble
Space Telescope's (HST) CALSPEC catalog to yield a final AFC error of 1.94\%
and total observation time of $\sim$22 minutes. Percent error accounts for
systematic uncertainties (filters, upstream optics, quantum efficiency) in
Roman component instrumentation along with shot noise for a signal to noise
ratio (SNR) of 500.
