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United States congressional apportionment is the process by which seats in the United States House of Representatives are redistributed amongst the 50 states following each constitutionally mandated decennial census. Each state is apportioned a number of seats which approximately corresponds to its share of the aggregate population of the 50 states. However, every state is constitutionally guaranteed at least one seat.


The number of seats in the House of Representatives is currently set to 435, and has been since 1913, except for temporary increase to 437 after the admission of Alaska and Hawaii. Though the actual reapportionment will normally occur in respect of a decennial census, the law that governs the total number of representatives and the method of apportionment to be carried into force at that time can be created prior to the census.

The decennial apportionment also determines the size of each state's representation in the U.S. Electoral College—that is, any state's number of electors equals the size of its total congressional delegation (i.e., House seat(s) plus Senate seats).

Federal law requires the Clerk of the House of Representatives to notify each state government of its entitled number of seats no later than January 25 of the year immediately following the census. After seats have been reapportioned, each state determines the boundaries of congressional districts—geographical areas within the state of approximately equal population—in a process called redistricting.

Constitutional text

The subject of representation is addressed twice in the Constitution. Originally, the apportionment of House seats was commanded by Article I, Section 2, clause 3, which states:

Following the end of the Civil War, the above provision was superseded by Section 2 of the Fourteenth Amendment, which states:

Article I additionally provides that:

House size

Ratio of representation in the House, 1789–1923
Years Source Constituents per Representative
1789–1793 U.S. Constitution 30,000
1793–1803 U.S. Census of 1790 33,000
1803–1813 U.S. Census of 1800 33,000
1813–1823 U.S. Census of 1810 35,000
1823–1833 U.S. Census of 1820 40,000
1833–1843 U.S. Census of 1830 47,700
1843–1853 U.S. Census of 1840 70,680
1853–1863 U.S. Census of 1850 93,425
1863–1873 U.S. Census of 1860 127,381
1873–1883 U.S. Census of 1870 131,425
1883–1893 U.S. Census of 1880 151,912
1893–1903 U.S. Census of 1890 173,901
1903–1913 U.S. Census of 1900 194,182
1913–1923 U.S. Census of 1910 212,407

The size of the United States House of Representatives refers to total number of congressional districts (or seats) into which the land area of the United States proper has been divided. The number of voting representatives is currently set at 435. There are an additional five delegates to the House of Representatives. They represent the District of Columbiamarker and the territories of American Samoamarker, Guammarker, the Northern Mariana Islandsmarker, which first elected a representative in 2008, and the U.S.marker Virgin Islandsmarker. Puerto Rico also elects a resident commissioner every four years. Proposals have been made to add voting representation for the District of Columbia, now represented only by a non-voting delegate (see below), who is not counted as one of the apportioned House representatives. Recent bills, such as the District of Columbia House Voting Rights Act of 2007, would resolve the issue by permanently increasing House membership to 437. One of the new members would be from the District of Columbia; the other would be from the next state in line to receive another House seat (as described below), presently Utahmarker.

Controversy and history

During the period that the current U.S. Constitution has been in effect, the number of citizens per congressional district has risen from an average of 33,000 in 1790 to almost 700,000 . Prior to the 20th century, the number of representatives increased every decade as more states joined the union, and the population increased. In 1911, Public Law 62-5 raised the membership of the U.S. House to 433 with a provision to add one permanent seat each upon the admissions of Arizonamarker and New Mexicomarker as states. As provided, membership increased to 435 in 1912.

But 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. Then in 1929 Congress passed the Reapportionment Act of 1929 which capped the size of the House at 435.

The U.S. population has increased more rapidly than the membership of the House of Represenatives.
The current size of 435 seats means one member represents on average about 650,000 people; but exact representation per member varies by state. Four states – Wyomingmarker, Vermontmarker, Alaskamarker and North Dakotamarker – have populations smaller than the average for a single district.

The ideal number of members has been a contentious issue since the country's founding. George Washington agreed that the original representation proposed in the Constitution Constitutional Convention (one representative for every 40,000) was inadequate and supported an alteration to reduce that number to 30,000. This was the only time that Washington pronounced an opinion on any of the actual issues debated during the entire convention. In Federalist No. 55, James Madison addressed the claims that the representation will be inadequate and proposes 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 forth 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." He also 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 proportionably 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 sceptre from reason."

The first proposed amendment to the Constitution attempted to set a pattern for growth of the House along with the population, but was never ratified. There has been debate over why the amendment was altered by a joint House and Senate subcommittee to cripple its chances for ratification.

Apportionment methods

Apart from the fact that the number of delegates is at least one for each state, as required by the Constitution, a state's number of representatives is in principle proportional to population thus assuring reasonably consistent representation to the people regardless of the state boundaries and populations. Though no method of calculating a fair distribution of voting power across the various states is possible because of the size of current electoral districts, five distinct apportionment methods have been used since the adoption of the Constitution, all of them susceptible to mathematical paradoxes.

The Method of Equal Proportions

The apportionment methodology currently used is the "Method of Equal Proportions", so called because it guarantees that no additional transfer of a seat (from one state to another) will reduce the ratio between the numbers of persons per Representative in any two states. According to, the method of equal proportions minimizes the percentage differences in the size of the congressional districts

In this method, as a first step, each of the 50 states is initially guaranteed at least one seat in the House of Representatives, leaving the remaining 385 seats to assign.

The remaining seats are allocated one at a time, to the state that "deserves" the next assigned seat the most. Thus, the 51st seat would go to the most populous state (currently California). The measure of how much a state "deserves" the next allocatable seat is determined by a priority formula that is mathematically computed to be 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. For instance, in the example above, California has already received a second seat and thus "deserves" another seat some measure less than it had before the second seat was assigned.

The formula for determining the priority of a state to be apportioned the next available seat defined by the method of equal proportions is

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

A_{n+1} = \sqrt{\frac{n}{n+2}} \ A_{n}

where n is still the number of seats the state has before allocation of the next, and for n = 1, the initial A1 is explicitly defined as

A_{1} = \frac{P}{\sqrt{2}}

Consider the reapportionment following the 2000 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. But 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 An of any other state. However, the 53rd goes back to California because its A2 priority value is larger than the An of any other state. The 54th seat goes to New York because its A1 priority value is larger than the An of any other state at this point. This process continues until all 435 seats have assigned (in 2000, just after the 13th seat for North Carolina was allocated, much to the chagrin of state officials in Utah). 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 when normally another state rises to the top of the list.

The Census 2000 Ranking of Priority Values shows the order in which seats 51–435 were apportioned after the 2000 Census, with additional listings for the next five priorities. North Carolinamarker was allocated the final (435th) seat. Utahmarker (priority list 436) missed a fourth seat by only 857 residents. Legal action by Utah to amend the results, citing irregularities in the North Carolina count and undercounting of Utah's overseas missionary population (suggested to be as many as 14,000), was unsuccessful. The proposed Voting Rights Act of 2007 would have granted Utah a fourth seat, as well as a voting Representative to the District of Columbia, had it passed.

Past apportionments

Projected changes following the 2010 census

The U.S. Census Bureau will conduct a comprehensive census in April 2010. Based on the populations counted in each state, the United States Congress will be reapportioned based on the Equal Proportions Method defined above. The total number of voting representatives is expected to remain at 435, assuming no legislation passes that would modify the apportionment process. Since the Census Bureau releases population estimates every year, projections have been made that predict the states' populations as of April 2010.

One study estimates that fourteen seats would shift between the states as follows:
Gain more

than one
Gain one Lose one Lose more

than one
Texasmarker +4

Arizonamarker +2

Floridamarker +2
Georgiamarker +1

Nevadamarker +1
South Carolinamarker +1

Utahmarker +1
Illinoismarker -1

Iowamarker -1

Louisianamarker -1

Massachusettsmarker -1

Michiganmarker -1
Minnesotamarker -1

Missourimarker -1

New Jerseymarker -1

New Yorkmarker -1

Pennsylvaniamarker -1
Ohiomarker -2

Other possible changes include California losing a seat, and North Carolina gaining one. In addition, Florida may gain only one seat, rather than two, and Oregon may gain a seat.

The 10-year national growth rate is 12.5%. In this estimate, the population of states losing seats grew at a slower rate and the population of states gaining seats grew at a faster pace. Louisiana is the only state losing a seat that is estimated to have lost population between 2000 and 2010, significantly due to the exodus precipitated by the damage caused by Hurricane Katrina. The losing states are in the industrial northeast and midwest, while gainers are in the southeast, southwest and Pacific northwest.

Past increases

The size of the U.S. House has increased as follows:


Date Size Comments
March 4, 1789 59 Seats provided for in the Constitution.
November 21, 1789 64 North Carolinamarker ratifies. Seats provided for in the Constitution.
May 29, 1790 65 Rhode Islandmarker ratifies. Seat provided for in the Constitution.
March 4, 1791 67 Vermontmarker admitted.
June 1, 1792 69 Kentuckymarker admitted.
March 4, 1793 105 Apportionment of the First Census.
June 1, 1796 106 Tennesseemarker admitted.


Date Size Comments
March 1, 1803 107 Ohiomarker admitted.
March 4, 1803 142 Apportionment of the Second Census.
April 30, 1812 143 Louisianamarker admitted.
March 4, 1813 182 Apportionment of the Third Census.
December 11, 1816 183 Indianamarker admitted.
December 10, 1817 184 Mississippimarker admitted.
December 3, 1818 185 Illinoismarker admitted.
December 14, 1819 186 Alabamamarker admitted.
March 15, 1820 186 Mainemarker admitted, given seven seats. Massachusettsmarker delegation reduced correspondingly.


Date Size Comments
August 10, 1821 187 Missourimarker admitted.
March 4, 1823 213 Apportionment of the Fourth Census.
March 4, 1833 240 Apportionment of the Fifth Census.
June 15, 1836 241 Arkansasmarker admitted.
January 26, 1837 242 Michiganmarker admitted.


Date Size Comments
March 4, 1843 223 Apportionment of the Sixth Census.
March 3, 1845 224 Floridamarker admitted.
December 29, 1845 226 Texasmarker annexed and admitted.
December 28, 1846 228 Iowamarker admitted.
May 29, 1848 230 Wisconsinmarker admitted.
March 4, 1849 231 Wisconsin given another seat.
September 9, 1850 233 Californiamarker admitted.
March 4, 1853 234 Apportionment of the Seventh Census.
May 11, 1858 236 Minnesotamarker admitted.
February 14, 1859 237 Oregonmarker admitted.


Date Size Comments
January 29, 1861 238 Kansasmarker admitted.
June 2, 1862 239 California awarded an extra seat.
March 4, 1863 241 Apportionment of the Eighth Census.
June 20, 1863 241 West Virginiamarker admitted; given three seats. Virginia's delegation reduced in census reapportionment.
October 31, 1864 242 Nevadamarker admitted.
March 1, 1867 243 Nebraskamarker admitted.
March 4, 1873 292 Apportionment of the Ninth Census.
August 1, 1876 293 Coloradomarker admitted.


Date Size Comments
March 4, 1883 325 Apportionment of the Tenth Census.
November 2, 1889 328 North Dakotamarker and South Dakotamarker admitted. One seat goes to the former, two to the latter.
November 8, 1889 329 Montanamarker admitted.
November 11, 1889 330 Washingtonmarker admitted.
July 3, 1890 331 Idahomarker admitted.
July 10, 1890 332 Wyomingmarker admitted.
March 4, 1893 356 Apportionment of the Eleventh Census.
January 4, 1896 357 Utahmarker admitted.


Date Size Comments
March 4, 1903 386 Apportionment of the Twelfth Census.
November 16, 1907 391 Oklahomamarker admitted.
January 6, 1912 393 New Mexicomarker admitted.
February 14, 1912 394 Arizonamarker admitted.
March 4, 1913 435 Apportionment of the Thirteenth Census. House size locked by Public Law 62-5, excepting temporary expansions due to the admission of new states.
January 3, 1959 436 Alaskamarker admitted.
August 21, 1959 437 Hawaiimarker admitted.
January 3, 1963 435 Apportionment of the Eighteenth Census. House size reverted to 435 per Public Law 62-5.

Proposed expansion

Expansion would cause the United States Electoral College result to more closely reflect the national popular vote, as the number of Representatives would begin to dwarf the number of Senators, which is fixed at two per state. The Wyoming Rule, an idea with some contemporary currency, calls for expanding the House until the standard Representative-to-population ratio equals that of the smallest entitled unit (i.e., Wyomingmarker). This proposal is primarily designed to address the fact that some House districts are currently nearly twice the size of others; for instance, there are about 944,000 residents in Montanamarker's single district, compared to about 515,000 in Wyoming's. See List of U.S. states by population.

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.

In 2007, the Utah delegation asked Congress to pass a bill that would add two seats to the House of Representatives, one for Utah and one for the District of Columbiamarker. A bill doing so passed the House but was blocked in the Senate. In 2009, the bill passed the Senate, but has not been voted on in the House because of an unrelated amendment. President Obama has said he would sign it. Should full representation of DC be found constitutional by the courts, the number of Representatives in the House would expand by two.

See also


  • Delegate counts in italics represent temporary counts assigned by Congress until the next decennial census or by the U.S. Constitution in 1789 until the first U.S. Census.
  • Elections held in the year of a census use the apportionment determined by the previous census.
  1. The populations of Washington, D.C. and federal territories are not included in this figure.
  2. U.S. Constitution, Article II, Section 1, Clause 2.
  3. Bush signs federalization bill, Agnes E. Donato, Saipan Tribune, May 10, 2008.
  4. George Will Called Me An Idiot, Jonah Golderg, National Review, January 15, 2001.
  5. The Federalist #55
  6. The Size of the U. S. House of Representatives and its Constituent State Delegations,
  7. ;
  8. House of Representatives? Hardly., Alcee Hastings, May 21, 2001.
  9. Senate Passes D.C. Voting Rights Bill, 61-37


Further reading

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