An apparatus and method for measuring feature sizes having form birefringence. The method includes providing a surface having surface features thereon; radiating the surface features with light having a first wavelength and a first polarization; measuring a reflected polarization of light having the first wavelength reflected from the surface features; rotating the surface features by rotating the surface to measure the reflected polarization of the reflected light having the first wavelength at least one new rotated position; radiating the surface features with light having a second wavelength and the first polarization; measuring a reflected polarization of light having the second wavelength reflected from the surface features; rotating the surface features by rotating the surface to measure the reflected polarization of the reflected light having the second wavelength at least one new rotated position; and correlating the reflected polarization from the light having the first and second polarizations to surface feature sizes.