  A charge modulation has recently been reported in (Y,Nd)Ba$_2$Cu$_3$O$_{6+x}$
[Ghiringhelli {\em et al.} Science 337, 821 (2013)]. Here we report Cu $L_3$
edge soft x-ray scattering studies comparing the lattice modulation associated
with the charge modulation in YBa$_2$Cu$_3$O$_{6.6}$ with that associated with
the well known charge and spin stripe order in La$_{1.875}$Ba$_{0.125}$CuO$_4$.
We find that the correlation length in the CuO$_2$ plane is isotropic in both
cases, and is $259 \pm 9$ \AA for La$_{1.875}$Ba$_{0.125}$CuO$_4$ and $55 \pm
15$ \AA for YBa$_2$Cu$_3$O$_{6.6}$. Assuming weak inter-planar correlations of
the charge ordering in both compounds, we conclude that the order parameters of
the lattice modulations in La$_{1.875}$Ba$_{0.125}$CuO$_4$ and
YBa$_2$Cu$_3$O$_{6.6}$ are of the same order of magnitude.
