Article I, Section 2, paragraph 3 of the U.S. Constitution states, in part: “The Number of Representatives shall not exceed one for every thirty Thousand, but each State shall have at Least one Representative;”, where there is, admittedly, some sketchy counting principles. There is no hint of help as to the limit at hand.

The number of representatives in the U.S. House changed every few years from 1789 through 1911.

The population of the USA has increased from roughly 4M in 1790, to roughly 90M in 1910, to roughly 300M in 2010.

The number of representatives was more or less set once and for all at 435 in 1911

My personal belief is based on my home/scratch work (not shown) regarding the two questions: How many people can one person reasonably represent? And: How many representatives can reasonably deliberate in one (such) body?

We’re talking a factor of three and a half since 1911,

TMBR

N.B. I am not affiliated with http://www.thirty-thousand.org/, and, for what it's worth, I came to this thought independently, years ago.