United States congressional apportionment

Since 1789, when the United States Congress first convened under the Constitution, the number of citizens per congressional district has risen from an average of 33,000 in 1790 to over 700,000 as of 2018. Prior to the 20th century, the number of representatives increased every decade as more states joined the union, and the population increased.

The ideal number of members has been a contentious issue since the country's founding. George Washington agreed that the original representation proposed during the Constitutional Convention (one representative for every 40,000) was inadequate and supported an alteration to reduce that number to 30,000.[8] This was the only time that Washington pronounced an opinion on any of the actual issues debated during the entire convention.[9] Five years later, Washington was so insistent on having no more than 30,000 constituents per representative that he exercised the first presidential veto in history on a bill which allowed half states to go over the quota.

In Federalist No. 55, James Madison argued that the size of the House of Representatives has to balance the ability of the body to legislate with the need for legislators to have a relationship close enough to the people to understand their local circumstances, that such representatives' social class be low enough to sympathize with the feelings of the mass of the people, and that their power be diluted enough to limit their abuse of the public trust and interests.

... first, that so small a number of representatives will be an unsafe depositary of the public interests; secondly, that they will not possess a proper knowledge of the local circumstances of their numerous constituents; thirdly, that they will be taken from that class of citizens which will sympathize least with the feelings of the mass of the people, and be most likely to aim at a permanent elevation of the few on the depression of the many; ...[10]

Madison also addressed Anti-Federalist claims that the representation would be inadequate, arguing that the major inadequacies are of minimal inconvenience since these will be cured rather quickly by virtue of decennial reapportionment. He noted, however,

I take for granted here what I shall, in answering the fourth objection, hereinafter show, that the number of representatives will be augmented from time to time in the manner provided by the Constitution. On a contrary supposition, I should admit the objection to have very great weight indeed.

Madison argued against the assumption that more is better:

Sixty or seventy men may be more properly trusted with a given degree of power than six or seven. But it does not follow that six or seven hundred would be proportionally a better depositary. And if we carry on the supposition to six or seven thousand, the whole reasoning ought to be reversed. ... In all very numerous assemblies, of whatever character composed, passion never fails to wrest the scepter from reason.[10]

When talking about the populations within California's reapportioned House districts in 1951, a report from Duke University found that "[there] is not an excessive disparity in district populations, but [the populations and disparities are] perhaps larger than necessary."[11] If the House continued to expand as it did prior to the Reapportionment Act of 1929, it would currently have 1,156 members (still just the second largest lower house, after China).[12] This would give the representatives, on average, about 287 thousand constituents, on par with Japan's National Diet.

The United States also has comparatively massive constituencies for OECD members, with almost three times more constituents per legislator on average than Japan and Mexico.[12] The U.S. has the third most populous average legislative districts in the world (second if the EU's European Parliament is not included).

The Apportionment Act of 1911 (Public Law 62-5) raised the membership of the U.S. House to 433 and provided for an apportionment. It also provided for additional seats upon the admissions of Arizona and New Mexico as states, increasing the number to 435 in 1912.

In 1921, Congress failed to reapportion the House membership as required by the United States Constitution. This failure to reapportion may have been politically motivated, as the newly elected Republican majority may have feared the effect such a reapportionment would have on their future electoral prospects.[13][14] A reapportionment in 1921 in the traditional fashion would have increased the size of the House to 483 seats, but many members would have lost their seats due to the population shifts, and the House chamber did not have adequate seats for 483 members. By 1929, no reapportionment had been made since 1911, and there was vast representational inequity, measured by the average district size. By 1929 some states had districts twice as large as others due to population growth and demographic shift.[15]

In 1929 Congress (with Republican control of both houses of Congress and the presidency) passed the Reapportionment Act of 1929 which capped the size of the House at 435 and established a permanent method for apportioning a constant 435 seats. This cap has remained unchanged since then, except for a temporary increase to 437 members upon the 1959 admission of Alaska and Hawaii into the Union.[16]

Two states, Wyoming and Vermont, have populations smaller than the average for a single district, although neither state has fewer people than the least populous congressional districts.

Among the Bill of Rights amendments to the United States Constitution proposed by Congress in 1789, was one addressing the number of seats in the House. It attempted to set a pattern for growth of the House along with the population, but has not been ratified.

After the first enumeration required by the first article of the Constitution, there shall be one Representative for every thirty thousand, until the number shall amount to one hundred, after which the proportion shall be so regulated by Congress, that there shall be not less than one hundred Representatives, nor less than one Representative for every forty thousand persons, until the number of Representatives shall amount to two hundred; after which the proportion shall be so regulated by Congress, that there shall not be less than two hundred Representatives, nor more than one Representative for every fifty thousand persons.[17]

Taken at face-value, with the nation's population reaching approximately 308.7 million according to the 2010 census, the proposed amendment would have called for an up-to 6,000-member House.[18][19][20] However, in the context of its original construction, the amendment may have instead outlined an iterative procedure for apportionment following a square root rule relative to the population (e.g. ${\textstyle Representatives\approx {\sqrt {10000+Population/100}}-100}$) that would still have called for a more than 1,600-member House following the same 2010 census.[21][22]

One proposal to alleviate the current constituency disparities and the high average number of constituents in many states' congressional districts is the "Wyoming rule." Operating similar to New Zealand's method of allocation for proportional representation, it would give the least populous state (which has been Wyoming since 1990) one representative and then create districts in other states with the same population.[23]

Another proposed expansion rule, the cube root rule,[24] calls for the membership of the legislature to be based on the cube root (rounded up) of the U.S. population at the last census. For example, such a rule would call for 692 members of the House based on the 2020 United States census. An additional House member would be added each time the national population exceeds the next cube; in this case, the next House member would be added when the census population reached 331,373,889, and the one after that at 332,812,558. A variation would split the representation between the House and the Senate, e.g. 592 members in the House (692 − 100 senators).[25]

On May 21, 2001, Rep. Alcee Hastings sent a dear colleague letter pointing out that U.S. expansion of its legislature had not kept pace with other countries.[26]

In 2007, during the 110th Congress, Representative Tom Davis introduced a bill in the House of Representatives that would add two seats to the House, one for Utah and one for the District of Columbia. It was passed by the House, but was tripped up by procedural hurdles in the Senate and withdrawn from consideration. An identical bill was reintroduced during the 110th Congress. In February 2009 the Senate adopted the measure 61–37. In April 2010, however, House leaders decided to shelve the proposal.[27]

Two provisions of Section 102, subsection (d) in the Washington, D.C., Admission Act by delegate Eleanor Holmes Norton and its same-titled Senate companion by Sen. Tom Carper, both introduced in 2021 and again in 2023 during the 117th and 118th Congresses, seek to amend Section 22(a) of the Reapportionment Act by adding one to the permanent House membership for a total of 436 representatives as the state of Washington, Douglass Commonwealth (i.e., Washington, D.C.) would have been entitled to an at-large district.[28][29] Holmes Norton's bill previously passed the House during the 116th Congress but not the Senate.[30]

The apportionment method currently used is the method of equal proportions, which minimizes the percentage differences in the number of people per representative among the different states.[46] The resulting apportionment is optimal in the sense that any additional transfer of a seat from one state to another would result in larger percentage differences.[47]

In this method, as a first step, each of the 50 states is given its one guaranteed seat in the House of Representatives, leaving 385 seats to assign. The remaining seats are allocated one at a time, to the state with the highest priority number. Thus, the 51st seat would go to the most populous state (currently California). The priority number is determined by the ratio of the state population to the geometric mean of the number of seats it currently holds in the assignment process, n (initially 1), and the number of seats it would hold if the seat were assigned to it, n+1. Symbolically, the priority number A_n is

${\displaystyle A_{n}={\frac {P}{\sqrt {n(n+1)}}}}$

where P is the population of the state, and n is the number of seats it currently holds before the possible allocation of the next seat. An equivalent, recursive definition is

${\displaystyle A_{m+1}={\sqrt {\frac {m}{m+2}}}\ A_{m}}$

${\displaystyle A_{n}={\sqrt {\frac {n-1}{n+1}}}\ A_{n-1}}$

where n is still the number of seats the state has before allocation of the next (in other words, for the mth allocation, n = m-1).

Consider the reapportionment following the 2010 U.S. census: beginning with all states initially being allocated one seat, the largest value of A₁ corresponds to the largest state, California, which is allocated seat 51. After being allocated its 2nd seat, its priority value decreases to its A₂ value, which is reordered to a position back in line. The 52nd seat goes to Texas, the 2nd largest state, because its A₁ priority value is larger than the A_n of any other state. However, the 53rd seat goes back to California because its A₂ priority value is larger than the A_n of any other state. The 54th seat goes to New York because its A₁ priority value is larger than the A_n of any other state at this point. This process continues until all remaining seats are assigned. Each time a state is assigned a seat, n is incremented by 1, causing its priority value to be reduced and reordered among the states, whereupon another state normally rises to the top of the list.

The 2010 census ranking of priority values[48] shows the order in which seats 51–435 were apportioned after the 2010 census, with additional listings for the next five priorities. Minnesota was allocated the final (435th) seat. North Carolina missed its 14th seat by 15,754 residents as the 436th seat to be allocated; ten years earlier it had gained its 13th seat as the 435th seat to be allocated based on the 2000 census.[49]

The 2020 census ranking of priority values[50] shows the order in which seats 51–435 were apportioned after the 2020 census, with additional listings for the next ten priorities. For the second time in a row, Minnesota was allocated the final (435th) seat. If either New York had registered 89 more residents or Minnesota had registered 26 fewer residents, New York would have been allocated the 435th seat instead.[51][52]