Lever rule
![A phase diagram with tie line (LS). The x dimension defines the percent weight of elements A and B.](/Images/godic/202501/24/Lever_rule.svg4943.png")
![Tie line in the Alpha plus Liquid two phase region](/Images/godic/202501/24/Eutectic_phase_diagram_Tie_Line4943.png")
The lever rule is a tool used to determine weight percentages of each phase of a binary equilibrium phase diagram. It is used to determine the percent weight of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus.