The proportion of each is determined by the lever rule.

The relative amounts of constituents are found using the lever rule.

The quantity of each phase is given by the lever rule (expressed in the variable corresponding to the x-axis, here mole fraction).

The lever rule is a tool used to determine weight percentages of each phase of a binary equilibrium phase diagram.

The proportion of ferrite and cementite forming above the eutectoid point can be calculated from the iron/iron-carbide equilibrium phase diagram using the lever rule.

The percent weight of element B at the liquidus is given by w and the percent weight of element B at the solidus is given by w. The percent weight of solid and liquid can then be calculated using the following lever rule equations: