Apportionment: dividing House seats among the states

Apportionment is the process of dividing the 435 seats in the U.S. House of Representatives among the 50 states after each census. The Census Bureau describes it as “distributing the 435 memberships, or seats, in the U.S. House of Representatives among the 50 states.” Seats are assigned by a formula called the method of equal proportions, adopted by Congress in 1941. Apportionment is separate from redistricting, the drawing of district lines within each state.

Definition

The Census Bureau’s definition is quoted above.⁠¹ The constitutional basis is Article I, Section 2, which provides that “Representatives and direct taxes shall be apportioned among the several states” according to population, and that “the actual Enumeration shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent term of ten years, in such manner as they shall by law direct”.⁠²

The apportionment population is not exactly the resident population. For 2020 it “includes the resident population of the 50 states,” plus overseas U.S. military and federal civilian personnel and their dependents who can be allocated to a home state.⁠³

Origin and history

The method has changed over time. The Census Bureau notes that five apportionment methods have been used since the first census in 1790, and that the current “Method of Equal Proportions” was “adopted by congress in 1941 following the census of 1940”.⁠⁴ Federal law, 2 U.S.C. 2a, requires the President to transmit to Congress “a statement showing the whole number of persons in each State” and the number of Representatives each state would receive “of the then existing number of Representatives by the method known as the method of equal proportions”.⁠⁵ The statute’s history lists the original 1929 act and the 1941 amendment providing “for reapportionment based on seventeenth and subsequent decennial censuses”.⁠⁵

How apportionment is calculated

The method of equal proportions works by priority values. The Census Bureau explains that “the priority value is determined by multiplying the population of a state by a ‘multiplier’”.⁠⁴ “Each of the 50 states is given one seat out of the current total of 435”.⁠⁴ Then, for each state’s nth seat, the multiplier is 1 divided by the square root of n times (n minus 1).⁠⁴ The 51st seat goes to the state with the highest priority value, that state’s next priority value is computed, and the process repeats; in the Bureau’s words, “this continues until all 435 seats have been assigned to a state”.⁠⁴

Hypothetical example. A state with 10 million people competing for its second seat has a multiplier of 1 divided by the square root of 2, about 0.707, giving a priority value of about 7.07 million. A state with 4 million people competing for its first additional seat has the same multiplier and a priority value of about 2.83 million. The larger state’s claim ranks higher.

After each census, some states gain seats and others lose them. The Census Bureau states that “some states will gain or lose seats in the U.S. House of Representatives based on 2020 Census population counts”.⁠¹

Common confusions and neighboring terms

• Apportionment vs. redistricting. Apportionment decides how many seats each state gets. Redistricting draws the boundaries of districts within a state, a job done by state legislatures or, in some states, by commissions.
• Apportionment vs. gerrymandering. Gerrymandering is a way of drawing district lines for advantage; it happens in redistricting, not apportionment.
• Apportionment vs. representation. Apportionment fixes the number of seats; representation concerns how seat holders act.

How My Vote Forward uses the term

My Vote Forward uses apportionment as an example of a fixed, published formula applied to public data: a model for how its own aggregates should state their methods. The framework does not compute or comment on apportionment results. Which authorities draw district lines is part of the Jurisdictions discussion.

Unresolved questions

• Should the current total of 435 House seats be revisited as population grows, and who should decide?
• How should disclosure protections in census data be balanced against accuracy for apportionment and redistricting?
• Which population should apportionment count, and how should disputes over that question be settled?