By statute, there are 435 members in the U.S. House of Representatives. But it doesn't have to be that way. Congress can, at any time, add new seats by statute. Unless major changes are made, the new ones would be awarded to states according to the same formula currently used, which is the most logical method.
In the formula, which you can see at right, P is a state's population and n is the number of seats it currently has. The state that produces the largest A value at any point in the process is next in line to gain its (n+1)th seat. The formula ensures at each point that the next seat added goes to the state that (1) is farthest from the average per district population AND (2) does not become farther from the average if it is given an additional seat.
Anyway, that's the boring math part. Here's the more interesting democracy part: It's probably a really good idea to add more seats, given that each member of a 435-man Congress is representing, on average, more than 700,000 constituents, whereas originally, the target was about 30,000 constituents per member. In Federalist Number 55, James Madison discussed the dangers of both a too-large Congress and a too-small one:
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. The truth is, that in all cases a certain number at least seems to be necessary to secure the benefits of free consultation and discussion, and to guard against too easy a combination for improper purposes; as, on the other hand, the number ought at most to be kept within a certain limit, in order to avoid the confusion and intemperance of a multitude. In all very numerous assemblies, of whatever character composed, passion never fails to wrest the sceptre from reason. Had every Athenian citizen been a Socrates, every Athenian assembly would still have been a mob.
One interesting idea, mentioned in a Wikipedia stub but barely anywhere else, is the so-called "Wyoming Rule," which proposes to add districts until the smallest single-district state (population 568,000) is not so badly over-represented. As it happens, you can get pretty close to that number (average 579,000) by adding exactly 100 districts.
I think this would be great, just because it would improve most people's representation. But I think the folks discussing this idea are confused on a number of levels. For one thing, Wyoming is not the most overrepresented state -- by a long way, that distinction goes to Rhode Island, with its two districts, average population 528,000.
Second, their discussion seems to suggest that an enlargement of the House would benefit Democrats because it would add clout to larger states like California. In fact, it would probably make little difference for either party. And large states like California and Texas are the least likely to benefit or suffer. Their large numbers of districts guarantee that they are always close to mean representation, no matter how large the House gets.
To give you some idea of how this all works out, I've calculated what Congress would look like if you added 100 seats. Here is the table:
||Pop. per seat, 2010||Population||New pop. per seat||New Number of seats||% Change in state's representation|
The most underepresented state in the House right now is Montana, where 994,000 people share a single congressman. If you added 100 seats to the Congress, Montanans would gain one seat and 63% percent more representation in Congress. Californians would lose a small amount of congressional clout.
Other small states like Alaska and South Dakota would suffer in a 535-member House. By the very nature of the process, small states are the most likely to win or lose big in reapportionment. The question of who wins or loses (Delaware, say, or South Dakota?) is really a random one, depending less on the mean population of the districts than on the exact point at which you stop awarding new seats. Someone is always going to be on the cusp of getting a new seat, and they're the ones most likely to lose or gain.