How large of a run would a dozen chickens need to be considered "pastured" for this discussion?
Pasture raised, like many of the other terms used to describe the way chickens are kept seems to vary depending on country and interpretation.
It's a bit like the term free range.
This is a picture of a major egg product concern and these chickens are described as pasture raised.
As you can see, not much pasture left.
Yes it is a lot better than the caged keeping conditions but...
I and other who have looked into this and made comparisons to the areas a jungle fowl family need to be self sufficient estimate an acre of ground per breeding pair.
But, jungle ecology and an average back yard or even an average farm are very different environments. The most obvious difference being that should the acre of jungle the breeding pair live off become insufficient in forage, the pair move on to another acre.
I used to free range four or five tribes/groups on very varied vegitation and still fed some commerciial feed. The amount these chickens ate of the commercial feed varied from season to season. If I was to make an informed guess I think it might have been possible for one of these tribes to survive on four acres.
One aspect that often gets overlooked is the breed of chicken and their knowledge of their environment. The first generation of say hatchery birds let loose to free range are likely to die quite quickly due to predation and food shortages left to fend for themselves.
Also, the breeds that tend to fare well free ranging don't lay many eggs and by USA standards wouldn't make a decent meal for one person.
Full free ranging as in only confined at night, or left to roost where they choose in just about any environment apart from a jungle or similar climatic ideal is a long term project, even with the right breeds. I headed towards this for ten years and still didn't get there with a mix of bantams and Marans.
I know a few people that have done it and it's taken generations in human terms, not chicken terms and they had the pick of some of the best free range capable chickens known.
The best you can hope for unless you wish to make chickens your lifes work is to free range them on whatever land you have available. Even then, they will need feeding, be that with commercial feed or a feed you make up yourself. You will also lose chickens like small change if you have any of the more persistant predators in the locality. It all looks like a wondefull idea on the internet, but the reality is hard on the keepers and even harder on the chickens.
If you can for example fence half an acre of ground which has trees, shrubs, bushes and varied vegitation you'll be doing better than many. You will still need to provide the chickens with feed. Hopefully when forage is good, you can reduce the feed costs, but that's about as good as it's going to get for the vast majority of people who just want to keep a few chickens for some eggs and possibly entertainment and they are wonderfully entertaining.