The paper presents a novel method for estimating the absolute quality of individual protein structure models, addressing a gap in current scoring functions that primarily focus on ranking alternative models of the same sequence. The authors introduce the QMEAN Z-score, which provides an estimate of the "degree of nativeness" of structural features in a model and indicates whether the model is of comparable quality to experimental structures. The QMEAN scoring function, based on six structural descriptors, is normalized with respect to the number of interactions, making it independent of protein size and suitable for assessing both monomers and oligomeric assemblies. The QMEAN Z-score is calculated by comparing the normalized QMEAN score of a model to distributions obtained from high-resolution X-ray structures. The method is validated through a comprehensive analysis of experimental structures in the PDB, demonstrating its ability to detect significant errors in experimental structures and evaluate theoretical models. The QMEAN Z-score also reveals that membrane proteins and thermophilic proteins exhibit distinct structural characteristics, with membrane proteins showing higher interaction energies and thermophilic proteins receiving significantly higher scores compared to mesophilic proteins. The QMEAN Z-score is integrated into the QMEAN server and is available for use in assessing the absolute quality of protein models.The paper presents a novel method for estimating the absolute quality of individual protein structure models, addressing a gap in current scoring functions that primarily focus on ranking alternative models of the same sequence. The authors introduce the QMEAN Z-score, which provides an estimate of the "degree of nativeness" of structural features in a model and indicates whether the model is of comparable quality to experimental structures. The QMEAN scoring function, based on six structural descriptors, is normalized with respect to the number of interactions, making it independent of protein size and suitable for assessing both monomers and oligomeric assemblies. The QMEAN Z-score is calculated by comparing the normalized QMEAN score of a model to distributions obtained from high-resolution X-ray structures. The method is validated through a comprehensive analysis of experimental structures in the PDB, demonstrating its ability to detect significant errors in experimental structures and evaluate theoretical models. The QMEAN Z-score also reveals that membrane proteins and thermophilic proteins exhibit distinct structural characteristics, with membrane proteins showing higher interaction energies and thermophilic proteins receiving significantly higher scores compared to mesophilic proteins. The QMEAN Z-score is integrated into the QMEAN server and is available for use in assessing the absolute quality of protein models.