The most birds I've had at once was about 22, but 4 were ducks who were a part of the chicken flock, and 4 were roosters. I've also had flocks of mixed ages. More than number of birds, having just adults of one species, with mostly girls, makes things a lot easier.
Now I just have chickens (and quail, but they are their own thing). I still have 4 roosters in a flock of about 16. It's too many roosters, luckily they are good breeds so I plan on selling a couple soon. Chicks are a lot of work too, so I've finally set limits on my broodiest hens
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Anyway in terms of just hens, I don't notice a big difference in work between 10 and 20. Less than 6 hens is too few to justify the time and money put into having chickens, IMO. My ideal number is probably between 12-18 hens, with half being older and half hatched into the flock every few years. That's enough that there's always some eggs and usually enough to give away. It's not so many that keeping up with feed is overwhelming.
Now I just have chickens (and quail, but they are their own thing). I still have 4 roosters in a flock of about 16. It's too many roosters, luckily they are good breeds so I plan on selling a couple soon. Chicks are a lot of work too, so I've finally set limits on my broodiest hens

Anyway in terms of just hens, I don't notice a big difference in work between 10 and 20. Less than 6 hens is too few to justify the time and money put into having chickens, IMO. My ideal number is probably between 12-18 hens, with half being older and half hatched into the flock every few years. That's enough that there's always some eggs and usually enough to give away. It's not so many that keeping up with feed is overwhelming.