Fluid dynamic gauging (FDG) is a non-contact technique for measuring the thickness and strength of fouling layers immersed in liquid in situ. These studies demonstrate its application to an annular geometry across a range of possible flow conditions, from stagnant to turbulent flow regimes (Reynolds number similar to 29,000). The results were not affected significantly by the surface under study being heated, indicating that the technique is suitable for measuring deposit thicknesses in situ during fouling experiments. Computational fluid dynamics simulations, which afford detailed information about the flow patterns and shear stresses imposed on the surface, showed good agreement with experimental data for tests in the laminar regime. A short study of whey protein fouling confirmed the feasibility of using FDG to monitor fouling layers.