A bench-top device fluid dynamic gauging device to study the swelling or shrinking of soft solid layers immersed in a liquid environment in situ and in real time is demonstrated. A particular feature is that the volume of liquid is isolated, hence the name Zero net discharge Fluid Dynamic Gauging (ZFDG), which renders ZFDG suitable for aseptic operation. For the 1.78 mm nozzle diameter used here, calibration tests gave a resolution of ±5 μm and uncertainty of ±10 μm. Computational fluid dynamics simulations indicated that the shear stress imposed on a layer being gauged differed between the successive suction and ejection stages in ZFDG. The swelling of polyvinyl acetate (PVA) layers (about 1 mm dry thickness) and gelatin films (50-80 μm dry thickness) in aqueous solutions is reported as demonstration of a ZFDG application. There was good agreement with more cumbersome gravimetric methods. Gelatin swelled noticeably faster at high pH, above the pKa values of proline and hydroxyproline. Fitting the gelatin swelling data to a power law model indicated ‘sub-Fickian’ behaviour with a ‘diffusion index’ which increased with pH.