  This is the fourth paper in a series studying star formation rates, stellar
components, metallicities, and star formation histories of a blue compact
galaxy (BCG) sample. Using Ha, [OII]3727, IR, radio (1.4GHz) luminosities and
neutral hydrogen gas masses, we estimated star formation rates(SFR) and gas
depletion timescales of 72 star-forming BCGs. The SFRs of the BCGs in our
sample span nearly four orders of magnitude, from approximately 10^-2 to
10^2M_sun/yr, with a median SFR of about 3M_sun/yr. The typical gas depletion
timescale of BCGs is about one billion years.
  We found that subtracting underlying stellar absorption is very important to
calculate both dust extinction and SFR of galaxies. Otherwise, the intrinsic
extinction will be overestimated, the SFRs derived from [OII] and Ha will be
underestimated (if the underlying stellar absorption and the internal
extinction were not corrected from the observed luminosity) or overestimated
(if an overestimated internal extinction were used for extinction correction).
After both the underlying stellar absorption and the dust extinction were
corrected, a remarkably good correlation emerges among Ha, [OII], IR and radio
SFR indicators. Finally, we find a good correlation between the measured SFR
and the absolute blue magnitude, metallicity, interstellar extinction of BCGs.
Our results indicate that faint, low-mass BCGs have lower star formation rates.
