The House has been fixed at 435 members since the 1910 census, when the country had about 92 million people. Pick a size, a census and an election, then see how seats, electors, voter weight and districting arithmetic move.
The slider moves from 435 to 1,000 in steps of 50. The named proposals set sizes between those steps, and they change with the census.
Each state has as many electors as it has House seats plus two senators, so a larger House shifts electors toward populous states. Replay an election at the chosen size.
The dashed lines mark a majority of electors and the Democratic share of the two-party popular vote.
Each election uses the census that governed it.
A state's electors divided by its people, compared with the national average. At 1.00 a resident carries average weight. The two electors every state gets for its senators lift small states above 1.00; adding House seats dilutes that bonus.
At the chosen sizeAt 435 seatsThin line marks 1.00
Does a larger House make gerrymandering harder? This page can compute the arithmetic of districting, which gives a mixed answer. It cannot draw maps, so the geographic argument is covered in the research summary below.
Even perfectly proportional maps must round to whole seats. This is the share of House seats lost to that rounding, summed across states.
The shaded band is the range of Democratic seat share a mapmaker could reach by packing and cracking with no geographic or legal limits. The line is the proportional share.
Fewest and most are the theoretical limits described under Methods, not forecasts.
Work by political scientist Jowei Chen on state legislatures found that swing states with more legislators per person show less evidence of gerrymandering. Smaller districts are more uniform inside, which leaves fewer competitive areas to pack and crack.
Jordan Ellenberg's account of Chen's findings on bigger legislatures
A simulation study of the 2020 redistricting cycle found partisan gerrymandering in many states, but the biases mostly offset nationally, netting Republicans about two seats. The larger cost was fewer competitive districts.
The 2023 PNAS study comparing enacted maps with simulated nonpartisan plans
The American Academy of Arts and Sciences modeled 265 House sizes and found little effect on which party controls the House, and no partisan effect on the Electoral College, while the small-state tilt shrinks. It recommends adding 150 seats.
The Academy's modeling of House expansion and partisan balance
Simulations by Magleby, Robinson and Walz suggest a larger House would not reduce polarization among members, though the increase levels off as the chamber grows. Smaller districts tend to be more one-sided.
Sources: Census Bureau apportionment tables for 2020 and 2010; the Census 2000 apportionment report to Congress; state presidential results from Federal Election Commission reports as compiled in FiveThirtyEight's election results dataset, cross-checked against MIT Election Data and Science Lab files.