We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to 100 nm. This table allows for easy and quick estimation of the concentration and size of modified and mono-dispersed silver nanoparticles from their optical spectra. We obtained data by determining the silver content of citrate-stabilised silver nanoparticles using sodium cyanide to dissolve the nanoparticles, and measuring solution conductivity with a pH meter and a cyanide-ion selective electrode. The quantification of the silver ion concentration enabled the calculation of extinction coefficients. Experimentally calculated extinction coefficients, in the current work, are in good agreement with collated literature values measured by different authors with non-standardized methodology and each for a limited range of particle size. They are also in good agreement with our theoretical calculations using Mie theory. Thus, we provide a highly standardized and comprehensive tabulated reference data-set.