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The allocation among states of the 435 seats in the United States House of Representatives changes each decade following the decennial United States Census. Each state is apportioned a number of seats based upon its population. This number also determines the state's number of electors in presidential elections, which equals the size of their congressional delegation (House plus Senate).

Reapportionment occurs every year ending in "1", the year after the decennial census. After seats have been reapportioned, each state determines the boundaries of Congressional districts within the state — geographical areas of approximately equal population — a process called redistricting.

Contents 1 House size 2 Apportionment methods 2.1 The Equal Proportions Method 3 State congressional delegation size 3.1 1789–1910 3.2 1920-present 4 Projected changes following the 2010 census 5 Notes 6 See also 7 External links

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	30,000
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 United States Constitution requires that

The number of Representatives shall not exceed one for every thirty thousand, but each state shall have at least one Representative (Article I, Section 2, Paragraph 3)

Prior to the twentieth century, the number of representatives increased every decade as more states joined the union, and the population increased.

In 1911, Public Law 62-5 set the membership of the U.S. House at 433; with the subsequent admission of Arizona and New Mexico as states, membership increased to 435, where it has remained (except for a brief period from 1959 to 1963 following the admission of Alaska and Hawaii, during which House membership was 437). If the ratio as specified by the Constitution of one representative for every 30,000 people were maintained today, the House of Representatives would have about 10,000 members. Instead, today one member represents about 650,000 people, which varies by state.

Proposals have been made to add voting representation for the District of Columbia, now represented only by a non-voting delegate, who is not counted as one of the 435 House representatives. A recent bill, the District of Columbia House Voting Rights Act of 2007, if passed, 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 Utah. The political appeal of this plan lies in its balancing of a new, presumably Democratic seat (D.C.) with a new likely Republican seat (Utah).

Apart from the fact that the number of delegates is at least 1 for each state, as required by the Constitution, a state's number of representatives is in principle proportional to population (thus equalizing the size of congressional districts nationwide). No method of calculating this desired result, however, has been found perfectly satisfactory in practice. Five distinct methods have been used since the adoption of the Constitution, all of them susceptible to mathematical paradoxes.

Further information: Huntington-Hill method

The so called "Equal Proportions method" is the apportionment methodology currently used. The method derives its name from the fact that it guarantees the property that no additional transfer of a seat (from one state to another) will reduce the percentage difference in per capita representation.

In this method, as a first step, each state is automatically guaranteed at least one seat in Congress. That means there are a total of 385 seats left to hand out.

The remaining seats are handed out one at a time, to the state that "deserves" another seat the most. Thus, the 51st seat always goes to the largest state (currently California).

The apportionment method uses a mathematical formula to express the priority ordering of states for an additional seat. For instance, in the example above, California has already received a second seat and thus "deserves" a third one less.

The formula used by the method of equal proportions is

where P is the population of the state, and n is the number of seats it currently has. An equivalent, recursive definition is

where n is still the number of seats the state has, and for n = 1, A is explicitly defined as

A sequential definition may likewise be given where the n = 1 case is defined as above, but the formula is

When all states have 1 seat, the largest value of A corresponds to the largest state. But now that California has 2 seats, its priority value decreases, and it has to take a step back in line. The 52nd seat goes to Texas, the 2nd largest state, but the 53rd goes back to California, and so on until all the seats have been handed out. Each time a state gets a seat, its priority drops and another state comes to the top of the list.

The Census 2000 Ranking of Priority Values^[1] shows the order in which seats 51–435 were apportioned after the 2000 Census, with additional listings for the next five priorities. North Carolina was allocated the final (435th) seat. Utah (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. However, Utah would have received a fourth seat if the District of Columbia House Voting Rights Act of 2007 had passed.

See also: Apportionment Bill

	1789	1790	1800	1810	1820	1830	1840	1850	1860	1870	1880	1890	1900	1910
Alabama	—	—	—	1	3	5	7	7	6	8	8	9	10	10
Arizona	—	—	—	—	—	—	—	—	—	—	—	—	—	1
Arkansas	—	—	—	—	—	1	1	2	3	4	5	6	7	7
California	—	—	—	—	—	—	2	2	3	4	6	7	8	11
Colorado	—	—	—	—	—	—	—	—	—	1	1	2	3	4
Connecticut	5	7	7	7	6	6	6	4	4	4	4	4	5	5
Delaware	1	1	1	2	1	1	1	1	1	1	1	1	1	1
Florida	—	—	—	—	—	—	1	1	1	2	2	2	3	4
Georgia	3	2	4	6	7	9	8	8	7	9	10	11	11	12
Idaho	—	—	—	—	—	—	—	—	—	—	1	1	1	2
Illinois	—	—	—	1	1	3	7	9	14	19	20	22	25	27
Indiana	—	—	—	1	3	7	10	11	11	13	13	13	13	13
Iowa	—	—	—	—	—	—	1	2	6	9	11	11	11	11
Kansas	—	—	—	—	—	—	—	—	1	3	7	8	8	8
Kentucky	—	2	6	10	12	13	10	10	9	10	11	11	11	11
Louisiana	—	—	—	1	3	3	4	4	5	6	6	6	7	8
Maine	—	—	—	7[2]	7	8	7	6	5	5	4	4	4	4
Maryland	6	8	9	9	9	8	6	6	5	6	6	6	6	6
Massachusetts	8	14	17	13[2]	13	12	10	11	10	11	12	13	14	16
Michigan	—	—	—	—	—	1	3	4	6	9	11	12	12	13
Minnesota	—	—	—	—	—	—	—	1	2	3	5	7	9	10
Mississippi	—	—	—	1	1	2	4	5	5	6	7	7	8	8
Missouri	—	—	—	—	1	2	5	7	9	13	14	15	16	16
	1789	1790	1800	1810	1820	1830	1840	1850	1860	1870	1880	1890	1900	1910
Montana	—	—	—	—	—	—	—	—	—	—	1	1	1	2
Nebraska	—	—	—	—	—	—	—	—	1	1	3	6	6	6
Nevada	—	—	—	—	—	—	—	—	1	1	1	1	1	1
New Hampshire	3	4	5	6	6	5	4	3	3	3	2	2	2	2
New Jersey	4	5	6	6	6	6	5	5	5	7	7	8	10	12
New Mexico	—	—	—	—	—	—	—	—	—	—	—	—	—	1
New York	6	10	17	27	34	40	34	33	31	33	34	34	37	43
North Carolina	5	10	12	13	13	13	9	8	7	8	9	9	10	10
North Dakota	—	—	—	—	—	—	—	—	—	—	1	1	2	3
Ohio	—	—	1	6	14	19	21	21	19	20	21	21	21	22
Oklahoma	—	—	—	—	—	—	—	—	—	—	—	—	5	8
Oregon	—	—	—	—	—	—	—	1	1	1	1	2	2	3
Pennsylvania	8	13	18	23	26	28	24	25	24	27	28	30	32	36
Rhode Island	1	2	2	2	2	2	2	2	2	2	2	2	2	3
South Carolina	5	6	8	9	9	9	7	6	4	5	7	7	7	7
South Dakota	—	—	—	—	—	—	—	—	—	—	2	2	2	3
Tennessee	—	1	3	6	9	13	11	10	8	10	10	10	10	10
Texas	—	—	—	—	—	—	2	2	4	6	11	13	16	18
Utah	—	—	—	—	—	—	—	—	—	—	—	1	1	2
Vermont	—	2	4	6	5	5	4	3	3	3	2	2	2	2
Virginia	10	19	22	23	22	21	15	13	11	9[3]	10	10	10	10
Washington	—	—	—	—	—	—	—	—	—	—	1	2	3	5
West Virginia	—	—	—	-	—	—	—	—	—	3[3]	4	4	5	6
Wisconsin	—	—	—	—	—	—	2	3	6	8	9	10	11	11
Wyoming	—	—	—	—	—	—	—	—	—	—	1	1	1	1
	1789	1790	1800	1810	1820	1830	1840	1850	1860	1870	1880	1890	1900	1910
Total:	65	106	142	186	213	242	232	237	243	293	332	357	391	435

	1920	1930	1940	1950	1960	1970	1980	1990	2000
Alabama	10	9	9	9	8	7	7	7	7
Alaska	—	—	—	1	1	1	1	1	1
Arizona	1	1	2	2	3	4	5	6	8
Arkansas	7	7	7	6	4	4	4	4	4
California	11	20	23	30	38	43	45	52	53
Colorado	4	4	4	4	4	5	6	6	7
Connecticut	5	6	6	6	6	6	6	6	5
Delaware	1	1	1	1	1	1	1	1	1
Florida	4	5	6	8	12	15	19	23	25
Georgia	12	10	10	10	10	10	10	11	13
Hawaii	—	—	—	1	2	2	2	2	2
Idaho	2	2	2	2	2	2	2	2	2
Illinois	27	27	26	25	24	24	22	20	19
Indiana	13	12	11	11	11	11	10	10	9
Iowa	11	9	8	8	7	6	6	5	5
Kansas	8	7	6	6	5	5	5	4	4
Kentucky	11	9	9	8	7	7	7	6	6
Louisiana	8	8	8	8	8	8	8	7	7
Maine	4	3	3	3	2	2	2	2	2
Maryland	6	6	6	7	8	8	8	8	8
Massachusetts	16	15	14	14	12	12	11	10	10
Michigan	13	17	17	18	19	19	18	16	15
Minnesota	10	9	9	9	8	8	8	8	8
Mississippi	8	7	7	6	5	5	5	5	4
Missouri	16	13	13	11	10	10	9	9	9
	1920	1930	1940	1950	1960	1970	1980	1990	2000
Montana	2	2	2	2	2	2	2	1	1
Nebraska	6	5	4	4	3	3	3	3	3
Nevada	1	1	1	1	1	1	2	2	3
New Hampshire	2	2	2	2	2	2	2	2	2
New Jersey	12	14	14	14	15	15	14	13	13
New Mexico	1	1	2	2	2	2	3	3	3
New York	43	45	45	43	41	39	34	31	29
North Carolina	10	11	12	12	11	11	11	12	13
North Dakota	3	2	2	2	2	1	1	1	1
Ohio	22	24	23	23	24	23	21	19	18
Oklahoma	8	9	8	6	6	6	6	6	5
Oregon	3	3	4	4	4	4	5	5	5
Pennsylvania	36	34	33	30	27	25	23	21	19
Rhode Island	3	2	2	2	2	2	2	2	2
South Carolina	7	6	6	6	6	6	6	6	6
South Dakota	3	2	2	2	2	2	1	1	1
Tennessee	10	9	10	9	9	8	9	9	9
Texas	18	21	21	22	23	24	27	30	32
Utah	2	2	2	2	2	2	3	3	3
Vermont	2	1	1	1	1	1	1	1	1
Virginia	10	9	9	10	10	10	10	11	11
Washington	5	6	6	7	7	7	8	9	9
West Virginia	6	6	6	6	5	4	4	3	3
Wisconsin	11	10	10	10	10	9	9	9	8
Wyoming	1	1	1	1	1	1	1	1	1
	1920	1930	1940	1950	1960	1970	1980	1990	2000
Total:	435	435	435	437	435	435	435	435	435

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 thirteen seats would shift between the states as follows:^[4]

• Texas +4
• Florida +2
• Arizona +2
• Georgia +1
• Utah +1
• Nevada +1
• Oregon +1
• Washington +1
• New York -2
• Ohio -2
• Massachusetts -1
• Pennsylvania -1
• Michigan -1
• Illinois -1
• Minnesota -1
• Iowa -1
• Missouri -1
• New Jersey -1
• Louisiana -1

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.^[4]

• 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.

• List of states ordered by number of electors in the presidential elections, which is two more for each state.
• United States Congress
• United States House of Representatives
• Alabama paradox
• Apportionment paradox
• Redistricting
• Gerrymandering
• List of U.S. states by population

• Congressional Apportionment by the U.S. Census Bureau
• Cut-the-knot.org:

• The Constitution and Paradoxes
• A Java Simulation of Adams' method
• A Java Simulation of Hamilton's method
• A Java Simulation of the Huntington-Hill method
• A Java Simulation of Jefferson's method
• A Java Simulation of Webster's method

• Thirty-thousand.org:

• A Brief History of Apportionment
• Forty or Thirty Thousand?
• The Size of the U. S. House of Representatives and its Constituent State Delegations Authorized Number of Seats by Year and by Congress 1789 to 2006
• Outcomes of Presidential Elections and the House Size