  We present {\it block analysis}, an efficient method to perform finite-size
scaling for obtaining the length scale of dynamic heterogeneity and the
point-to-set length scale for generic glass-forming liquids. This method
involves considering blocks of varying sizes embedded in a system of a fixed
(large) size. The length scale associated with dynamic heterogeneity is
obtained from a finite-size scaling analysis of the dependence of the
four-point dynamic susceptibility on the block size. The block size dependence
of the variance of the $\alpha$-relaxation time yields the static point-to-set
length scale. The values of the obtained length scales agree quantitatively
with those obtained from other conventional methods. This method provides an
efficient experimental tool for studying the growth of length scales in systems
such as colloidal glasses for which performing finite-size scaling by carrying
out experiments for varying system sizes may not be feasible.
