How did they come up with the number for the house of representatives?

The number of representatives in the U.S. House of Representatives, currently set at 435, was established by the Reapportionment Act of 1929. This act capped the number of representatives and mandated that seats be apportioned among the states based on population, as determined by the decennial census. The goal was to ensure proportional representation while maintaining a manageable size for the House. Adjustments to the number of representatives can occur after each census, but the cap has remained at 435 since the 1930s.