How many voting members does the U.S. House of Representatives have?

How to get close to this number

Derive it from the electoral college. The college totals 538, which is the House plus the Senate plus three for the federal district. Subtract a hundred senators and three district votes and you have the House. Two figures on this site define each other, and knowing either gives you the other by subtraction.

The fixed cap is the fact people find surprising. The chamber has not grown with the population since 1929, so the number of constituents each member represents has roughly tripled since then. A legislature of constant size in a growing country means representation gets steadily thinner, which is a structural consequence of a number that looks merely administrative.

Reapportionment is what keeps it interesting: seats shift between states after each census while the total stays capped, so states gain and lose representation at each other's expense rather than in absolute terms. A fixed-size chamber turns demographic change into a zero-sum political contest, which is a direct consequence of the cap.