Ammonia nitrogen, particularly in its free form (NH3), is a major inhibitor in the anaerobic digestion of organic wastes. Besides its importance, a wide variation in the reported inhibitory limits exists. This study aimed at calculating different inhibitory limits using data retrieved from the literature, unifying the presented results and linking them to the operational conditions and the main archaeal populations. The application of a logarithmic inhibition curve grouped literature results in five different inhibition coefficients (IC50), from 32 to 2,735 mg NH3-N·L-1. Increasing IC50 values were associated to higher pH values and temperatures, being the total ammonia nitrogen similar for all the curves obtained. In the experiments with low inhibition limits, acetotrophic archaea were dominant while hydrogenotrophs prevailed at higher IC50 values. For the first time, inhibitory values that can be linked to general AD conditions (i.e. operational parameters and microbial communities) are given, which can be used as a predictive tool towards monitoring of ammonia inhibition.