The determination of the interdetector volume (IDV) in size-exclusion chromatography (SEC) of polymers with dual multiangle light-scattering/concentration detection based on the s-detection is demonstrated. By s-detection the determination is meant of local molecular mass from a known relation between molecular mass and radius of gyration, obtained from the angle dependence of the intensity of scattered light. IDV is found basing on the stipulation of equal slope of local calibrations found by the dual light-scattering/concentration detection, referred to as the w- and s-detection. As the s-detection uses just the light-scattering detector and, therefore, is independent of the value of IDV, this quantity can be found by searching for its value that gives the local calibration dependence obtained by the dual detection closest to that determined independently by the s-detection.