page_title: Lever rule
section_title: Calculations
hierarchical_section_title: Lever rule / Calculations
context_page_description: The lever rule is a rule used to determine the mole fraction or the mass fraction of each phase of a binary equilibrium phase diagram. It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line.
  In an alloy or a mixture with two phases, α and β, which themselves contain two elements, A and B, the lever rule states that the mass fraction of the α phase is
  where
  is the mass fraction of element B in the α phase
  is the mass fraction of element B in the β phase
  is the mass fraction of element B in the entire alloy or mixture
  all at some fixed temperature or pressure.
caption: A phase diagram with tie line (LS) for a binary isomorphous system. The x dimension defines the mass fraction of elements A and B.