  We present our results on the electromagnetic form factor of pion over a wide
range of $Q^2$ using lattice QCD simulations with Wilson-clover valence quarks
and HISQ sea quarks. We study the form factor at the physical point with a
lattice spacing $a=0.076$ fm. To study the lattice spacing and quark mass
effects, we also present results for 300 MeV pion at two different lattice
spacings $a=0.04$ and 0.06 fm. The lattice calculations at the physical quark
mass appear to agree with the experimental results. Through fits to the form
factor, we estimate the charge radius of pion for physical pion mass to be
$\langle r_{\pi}^2 \rangle=0.42(2)~{\rm fm}^2$.
