The electronic and excitonic confinement of monoclinic silver sulfide Ag2S nanocrystals (NCs) has been investigated both theoretically and experimentally. Theoretically, the electronic band gaps and the excitonic ground-state energies of Ag2S NCs at different sizes are calculated using a hybrid method of density-functional theory (DFT) and effective mass approximation (EMA). The results have shown a good agreement with measured results, including the absorbance and photoluminescence spectra of drop-casted NC thin films. The Ag2S NCs, synthesized using wet-chemistry methods, have demonstrated a desirable size monodispersion, allowing the measurements to be sufficiently accurate. The results show that both the electronic band gap and the excitonic energy have significant blue shift only when the diameter of monodispersed NCs is reduced below 4 nm, and the excitonic Bohr radius of Ag2S is determined as being small at around 1 nm.