The rule of thumb for run size is 10 sq ft (1 sq m) per bird. More if your coop is pretty minimal in size, meaning that they already don’t have a lot of space. Potentially less if your flock spend each and every day, all day, yard-ranging or free ranging and therefore don’t use their run all that much except during crappy weather.
The example I usually post is that of a mid-sixties US station wagon with mom, dad, and six kids. In the summer. With insufficient air conditioning. “Mom, he keeps looking at me!” “Dad, she keeps poking me!” “Mommmm!” “Daaaaad!”
Chickens like to flock up to a point, but sometimes they just need more space. Your best chance for a happy flock with minimal drama is space, space, space.
No kidding; this is huge: your best chance for happy, low-drama chicken-keeping is what seems like a ridiculous amount of space. Irritable, fussy, overcrowded hens/ pullets are a recipe for disaster.