A 100kg person (so 220lb) would require 80gr protein with this RDA; so 1gr/lb would be 3 times RDA (whereas 0.5g would be 110g protein so only 1.4 RDA)

The 1g/kg is easy to remember, as is 0.5g/lb ; they are 120-140% of recommended for a sedantry lifestyle, but only 60-80% of what’s recommended for an athlete - so I use them as an easy to remember back-of-the-envelope numbers.

RDA is much less precise and scientific than one would think; it basically means “we know there are no serious defincies or overdoses if you keep this forever” - but they are not optimized for anything else; e.g. higher dose vitamin C was shown to shorten common cold recovery, and higher dose vitamin D with generally better everything.