  We propose a new improved model-independent method for calculating the pion
charge radius. In a recently-proposed model-independent method for the pion
charge radius, we find it difficult to compute the pion charge radius for small
pole mass $M_{\rm{pole}}^2$ and volume due to systematic errors coming from
finite volume effect and higher-order contamination of the Taylor expansion of
the form factor. We circumvent this difficulty by introducing a new appropriate
function and propose a modified method that can calculate the pion charge
radius with less systematic errors in the small $M_{\rm{pole}}^2$ and volume
cases. As preliminary results, we check that our improved model-independent
method works well on a mockup data and also an actual lattice QCD data at the
pion mass of 0.51 GeV.

High Energy Physics - Lattice