The planner you found will probably be the best tool for working this out but to answer the question...
Each animal will consume roughly the equivilant of one patch of grass a day, but that will often be from several patches in small amounts, so a single chicken in a field of grass wouldn't eat enough for you to even notice some of the taller grass is now a little shorter.
For larger numbers of animals the measurement is always how much more grass will grow, rather than how much you have and that is all about how much blank space there is for it to grow into. Each individual patch of grass tries to spread in at least one direction each day, but if that tile is occupied by anything it will fail, and not spread. This is a mechanic used for a lot of things in stardew valley.
If you had enough grass that it had a little over 24 open spaces around it most of the time, then it would be enough to consistently feed all your animals, but if you just had 24 patches of grass in one block it would be eaten up very quickly. Try to avoid small fenced in area's of grass for this reason.
Lots of small patches works well without using up much room, or one large patch, even if it is a bit further away, as long as the animals have a clear patch to it.
Source: Buying far to many grass starters without realising how to use them myself, before working out that they all want ample room around them to spread into.