Dendrimersomes are stable, monodisperse uni-lamellar vesicles self-assembled in water from amphiphilic Janus dendrimers. Their size, stability, and membrane structure are determined by the chemical structure of Janus dendrimer and the method of self-assembly. Comparative analysis of the periodic arrays in bulk and dendrimersomes assembled by ethanol injection in water of 11 libraries containing 108 Janus dendrimers is reported. Analysis in bulk and in water was performed by differential scanning calorimetry, X-ray diffraction, dynamic light scattering, and cryo-TEM. An inverse proportionality between size, stability, mechanical properties of dendrimersomes, and thickness of their membrane was discovered. This dependence was explained by the tendency of alkyl chains forming the hydrophobic part of the dendrimersome to produce the same local packing density regardless of the branching pattern from the hydrophobic part of the dendrimer. For the same hydrophobic alkyl chain length, the largest, toughest, and most stable dendrimersomes are those with the thinnest membrane that results from the interdigitation of the alkyl groups of the Janus dendrimer. A simplified spherical-shell model of the dendrimersome was used to demonstrate the direct correlation between the concentration of Janus dendrimer in water, c, and the size of self-assembled dendrimersome. This concentration-size dependence demonstrates that the mass of the vesicle membrane is proportional with c. A methodology to predict the size of the dendrimersome based on this correlation was developed. This methodology explains the inverse proportionality between the size of dendrimersome and its membrane thickness, and provides a good agreement between the experimental and predicted size of dendrimersome.