This study examines Turkey’s economic and diplomatic position within the Economic Cooperation Organization (ECO) through the lens of liberal international relations theory and tests the contribution of regional integration to the country’s process of becoming a global actor. The magnitude of “650 million people and five trillion dollars,” frequently repeated in the literature on ECO, has often been presented as if it were a present reality, yet it has never been tied to a concrete model or a measurable projection. To close this gap, the study adopts a theory-testing, mixed-methods (quantitative–qualitative) design; drawing on the population, income, and trade data of the member states, it constructs a three-scenario projection—baseline, moderate, and deep integration—and compares its findings against the European Union and ASEAN. The findings show that, although ECO brings together roughly seven percent of the world’s population, its share of world trade remains around two percent; while intra-organizational trade accounts for only one-tenth of the member states’ total foreign trade, this ratio exceeds sixty percent in the European Union and twenty-five percent in ASEAN. The five-trillion-dollar threshold at current prices is attainable only under the deep-integration scenario and only toward the mid-2030s, whereas at purchasing power parity this magnitude has already been surpassed. The study establishes that the organization’s true constraint is not geographic size but institutional depth, and that size can be converted into economic power only through common rules, connectivity, and financial coordination. Within this framework, the full implementation of ECOTA, the coordination of customs facilitation with Middle Corridor investments, the strengthening of the ECO Trade and Development Bank, and the redesign of the decision-making order are identified as priority policy areas. The results indicate that Turkey’s use of its anchor-state position by spearheading institutionalization would strengthen both regional stability and the country’s capacity for global actorness.