zeta potential measurements were used to determine the adsorbed layer thickness of poly(ethylene oxide)-polypropylene oxide-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers at the surfaces of poly(dimethylsiloxane) emulsion droplets, silica particles, and polystyrene latex particles. The adsorbed layer thickness (delta) was shown to depend on the copolymer structure, the surface chemistry of the adsorbent, and the level of cross-linking within droplets. For a wide range of copolymers, delta values are in the range 2-20 nm and directly proportional to the PEO block length. For copolymers with PEO segment lengths z PPO segment lengths, the plateau delta values for PDMS, latex, and silica correspond to similar to 35%, 20%, and 7% of the fully extended PEO segment length. Equivalent values for copolymers with PEO segment lengths < PPO segment lengths are significantly greater but follow the same dependence on the type of adsorbent. As the level of internal cross-linking within the PDMS droplets was increased, the interface became less deformable and the adsorbed copolymer layer thickness significantly decreased. Findings are discussed with respect to the adsorbed copolymer conformations, which result from different adsorption mechanisms and the influence of interfacial penetrability.