Scalability experiments on the spark plasma sintering (SPS) of similarly shaped alumina specimens of the four different sizes are conducted. The utilized experimental methodology, based on the principle of rigorous proportionality of all the specimen and tooling dimensions, employs two different SPS devices of different scales. The processed specimens are characterized in terms of relative density and grain-pore structure. Overall, SPS shows good scalability potential within a single SPS device, but indicates substantial structure changes when switching between different SPS devices. Despite deviations in some cases, by and large, the experimental results obtained for different tooling sizes and temperature regimes are rather similar for specimens processed by the same SPS device. The obtained density and grain size spatial distributions are relatively uniform. High final densities with moderate grain growth are common. At the same time, due to the demonstrated possibility of a significant size impact in case of high heating rates and large specimen sizes, as well as the demonstrated differences of the processing outcomes based on different SPS devices, the predictive capability of reliable modeling approaches is of great importance for the industrial implementation of SPS techniques.