Single-chain nanoparticles (SCNPs) constructed via reversible bonds are versatile stimuli-responsive soft nano-objects with potential use in nanomedicine, bioimaging, biosensing, and catalysis applications. In recent years, many different types of reversible SCNPs have been reported involving intrachain hydrogen bonding, host guest interactions, and metal complex formation, among other reversible bonds. As illustrated in this work, reversible SCNPs in solution with similar nature, molar mass, and amount of reactive groups than irreversible (covalent-bonded) SCNPs display, on average, a lower level of chain compaction. We follow herein a Flory-like argument to obtain a simple expression providing the expected size reduction upon folding single chains of size R-0 to SCNPs of size R with reversible interactions. Accurate estimation of R is Of outmost importance for developing practical applications of responsive SCNPs based on structure property relationships. For precursor chains having a fraction of groups x involved in reversible bonds, the expected size upon intrachain folding of the precursor chains to conventional SCNPs is given by R-0 = R-0 (1 - x)(0.6). We perform.a comparison of the size reduction predicted by the former expression with extensive literature data for SCNPs constructed via reversible bonds (72 SCNPs, 22 reversible interactions). The overall agreement between theoretical and experimental data is excellent, hence allowing a valuable a priori estimation of the size reduction upon folding single chains to single-chain nanoparticles via reversible interactions.