Planktonic foraminiferal shell weight has been widely used as a proxy for past ocean carbonate chemistry and calcification intensity; however, its interpretation remains complicated by biological, ecological, and diagenesis influences. This study reviews the methodological foundations, environmental controls, and inherent biases associated with shell-weight based proxies in paleoceanography. We evaluate traditional sieve-based approaches alongside measurement based methods, area density normalisation, micro-computed tomography (micro-CT), and dissolution-corrected initial size-normalised weight (ISNW), highlighting their relative strengths and limitations. Evidence from global datasets suggests that carbonate ion concentration primarily controls calcification under specific conditions. In many regions, particularly those influenced by monsoons and tropical oceans, temperature, productivity, food availability, species-specific ecology, and depth habitat exert stronger influences on shell mass than carbonate chemistry alone. Micro-CT studies further reveal compensatory strategies that preserve external test size despite reduced calcite volume, potentially masking changes in calcification when weight-based metrics are used in isolation. Post-depositional dissolution near the lysocline significantly overprints primary calcification signals, especially in the Indian and Southern Oceans. Overall, planktonic foraminiferal shell weight represents an integrated signal of environmental, ecological, and diagenetic processes rather than a single geochemical control. Robust paleoceanographic reconstructions therefore require species-specific analyses, advanced measurement techniques, and explicit correction for dissolution effects.