Productivity Research Notes (PRN Series), No. 2604. This note develops a bottom-up approach to measuring labor share in economies where compensation of employees (COE) is not available in national accounts, using Vietnam as a case study. By integrating micro-level data on wages, employment, and hours worked, it constructs consistent time-series estimates of labor compensation and factor income shares. The results show that the derived labor share aligns with available benchmark aggregates while remaining conceptually distinct from mixed income measures. The analysis further demonstrates that uncertainty in labor share measurement translates directly into substantial variation in total factor productivity (TFP) estimates, underscoring the importance of reliable labor compensation data for growth accounting in developing economies.