Nowadays the Fourier shell correlation (FSC) is the most common method for estimating the resolution of 3D structures obtained in Single Particle Imaging (SPI) experiments on X-ray free electron lasers (XFELs). In FSC, the resolution is defined as the spatial frequency at which the correlation between two independently reconstructed structures is equal to some given threshold value. There are multiple methods to define the threshold value. In addition, this approach cannot account for the fact that the quality of reconstruction can be on-uniform for different areas of the biomolecule. Thus, the issue of effective resolution estimation methods remains open. This paper considers multiple alternative approaches to the resolution estimation from adjacent scientific field-cryogenic electron microscopy (cryo-EM) and analyzes the applicability of these approaches to the resolution estimation in SPI experiments on XFELs. © 2020 CEUR-WS. All rights reserved.