Start with the total U.S. population, then divide by 100, since that’s the size of the current, more deliberative upper chamber. Next, allocate senators to each state according to their share of the total; 2/100 equals two senators, 3/100 equals three, etc. Update the apportionment every decade according to the official census.
“Here’s How To Fix the Senate” – The Atlantic
Using 2017 census estimates as a proxy for the official one coming in 2020, the Rule of One Hundred yields the following outcome: 26 states get only one senator (having about 1/100 of the population or less), 12 states stay at two, eight states gain one or two, and the four biggest states gain more than two: California gets 12 total, Texas gets nine, and Florida and New York get six each. This apportionment shows how out of whack the current Senate has become.