How is the volume of oil in a transformer determined?

Oil volume is determined from manufacturer data such as drawings, filling charts, and nameplate documentation, because tank geometry and radiators vary widely. During filling or draining, volume can be measured using calibrated flow meters, weigh scales, or tank level versus volume curves. For conservator units, separate volumes exist for main tank, radiators, and conservator. Accurate volume determination matters for purchasing oil, sizing containment, planning transport weight, and ensuring the expansion space and nitrogen blanket or breather system function correctly.