•Rapid determination of molecular weight of chitosanes was possible.•Single point determination of viscometric parameter for chitosanes was proposed.•Equations for quick viscometric measurements for chitosanes was evaluated. A viscometric study was carried out at 25°C to assess the physical–chemical behavior in solution and the mean viscometric molar mass (M¯v) of chitosan solutions with different deacetylation degrees, in two solvent mixtures: medium 1—acetic acid 0.3mol/L and sodium acetate 0.2mol/L; and medium 2—acetic acid 0.1mol/L and sodium chloride 0.2mol/L. Different equations were employed, by graphical extrapolation, to calculate the intrinsic viscosities η and the viscometric constants, to reveal the solvent's quality: Huggins (H), Kraemer (K) and Schulz–Blaschke (SB). For single-point determination, the equations used were SB, Solomon–Ciuta (SC) and Deb–Chanterjee (DC), resulting in a faster form of analysis. The values of ̄M¯v were calculated by applying the equation of Mark–Houwink–Sakurada. The SB and SC equations were most suitable for single-point determination of η and ̄M¯v and the Schulz–Blachke constant (kSB), equal to 0.28, already utilized for various systems, can also be employed to analyze chitosan solutions under the conditions studied.