We report a general method, based on intramolecular spin diffusion, for the measurement and calculation of spin-diffusion coefficients in amorphous polymers and their blends using only NMR data. The basic structural unit that defines H-1 polarization density in polymers is the monomer unit. Using appropriately selected internal reference distances calculated from energy-minimized chain dimension simulations, time scales for the redistribution of H-1 polarization within amorphous homopolymers may be used to independently calculate maximum values of the spin-diffusion coefficients D. This strategy represents an attractive alternative to current methods employed for domain size measurements in polymer blends, which require calibration of spin-diffusion coefficients based on comparisons of similar NMR data obtained on model compounds analyzed previously using scattering or microscopy techniques. In this way, many more polymer systems become amenable to study by NMR spin-diffusion methods, since X-ray scattering or microscopy calibrations on representative standards are no longer necessary to define quantitative limits on spin-diffusion coefficients. Experimentally, the fate of proton magnetization is followed with high selectivity using 2D H-1-C-13 solid-state HETCOR sequences incorporating controlled periods of H-1-H-1 spin diffusion.