A farmer living in Israel in Temple times would have given as follows:
- Approximately 2% of his crops to the Kohen (priest); known as teruma.
- 10% of his remaining crops to the Levite; ma'aser which means "tithing." (The Levite would then tithe that -- i.e. ~1% of the original crop -- and give it to the Kohen.)
- 10% of what's still remaining; depending on the year (there's a cycle), this is either given to the poor, or consumed by the farmer himself in Jerusalem.
- First fruits (that's not that many, quantity-wise; it's more about the significance) to the Kohen, at the Temple.
- The growth from his vineyard's fourth year would have to be consumed (by the owner) in Jerusalem.
- A "corner" (of some size) of a grain field should be left for the poor; as should random dropped sheaves or the occasional forgotten bundle. Similar laws apply to vineyards. (Once again this one, as I understand it, isn't so much about the quantity as it is about behavior modification.)
- A small piece (~5%) of dough, when kneading, is given to the Kohen.
And from livestock (cows, sheep, goats):
- Firstborn cows, sheep, and goats are given to the Kohen. Firstborn donkeys necessitate a lamb given to the Kohen. At first glance it looks like a cow will have about ten calves over her lifetime, so this is approximately 10%, if you're keeping count.
- Of the remaining flock, 10% must be consumed in Jerusalem.
When slaughtering an ordinary animal not as a sacrifice, the jaws, foreleg, and chest are given to a Kohen.
One lamb/kid consumed by its owners for Passover offering, in Jerusalem. Though many people can go in on this, as long as each person gets two ounces or so of meat.
- Some extra offering when visiting for the holidays; but again, you can go in with others for this (or even "be a total parasite", as a teacher of mine explained).
- The occasional offerings for sin atonement, as needed (hopefully not).
- An annual half-shekel to cover the Temple's communal offerings.
So if Farmer Asher grew 100 bushels of wheat, he'd wind up with -- oh, let's say about 75 bushels with which he could do anything; plus 8 bushels that will either go to the poor, or Farmer Asher should eat himself in Jerusalem, depending on the year.
Now Jacob promised G-d "all that you give to me I shall definitely tithe to you"; so for the non-agarian, non-Temple times, non-Israel dweller, the strongly normative and recommended practice (and while debated, we conclude it's not quite an obligation per se) is to give 10% of one's profits to charity. Giving up to 20% is considered meritorious; beyond that is not recommended as one risks putting themselves into poverty.