How much better off would the average person be if we took away enough money from the top 1% to make them no richer than the average person?
I assume the following:


We redistribute wealth (not income) from the top 1% to the bottom 99%
Everybody among the bottom 99% receives the same amount.


Source for my data: World Income Database

In 2014, the average personal net wealth among the top 1% was around \$11 million in 2017 prices. The total wealth to be distributed is hence (3.3 million people in the top percentile $\times$ 11 million) = \$36.3 trillion ($3.63\times10^{13}$).

This means that everybody among the bottom 99% receives around \$111,000. How much this makes you better off depends on your initial state. Concepts of low- and middle-class are somewhat ambigious. According to the WID data, net personal wealth among the bottom 50% is essentially zero, and \$205,000 among the 50 to 90th wealth percentile.

EDIT:

Please note that this is a purely mechanical and unrealistic exercise. For starters, it ignores legal and administrative hurdles. A major concern is also that a substantial share of the private wealth of the top 1% is invested in productive firms which employ millions of people. What happens  to their employees if you expropriate the owners of these firms?