  We present metallicity dependent transformation equations between UBV and
SDSS ugr colours for red giants with synthetic data. The ranges of the colours
used for the transformations are 0.400 $\leq(B-V)_{0}\leq$ 1.460, -0.085$\leq(U
- B)_{0}\leq$ 1.868, 0.291$\leq(g-r)_{0}\leq$ 1.326, and 1.030$\leq(u -
g)_{0}\leq$ 3.316 mag, and cover almost all the observational colours of red
giants. We applied the transformation equations to six clusters with different
metallicities and compared the resulting $(u - g)_{0}$ colours with the ones
estimated by the calibration of the fiducial sequences of the clusters. The
mean and standard deviation of the residuals for all clusters are $<\Delta(u -
g)_0> =$-0.01 and $\sigma(u - g)_{0} =$0.07 mag, respectively. We showed that
interstellar reddening plays an important role on the derived colours. The
transformations can be applied to clusters as well as to field stars. They can
be used to extend the colour range of the red giants in the clusters which are
restricted due to the saturation of SDSS data.
