The Pilling-Bedworth Ratio for Fe3O4 (magnetite) is 2.1 when compared to iron (Fe). This ratio indicates the relationship between the volume of the oxide and the volume of the metal. For further information, one can search terms like "Pilling-Bedworth ratio," "iron," and "magnetite" online. A relevant source for detailed insights is available at the provided link to a thesis document. Understanding this ratio is essential for applications involving magnetite in various fields.