Quota is the term used for the smallest number of votes that will guarantee the election of a candidate.
In a first-past-the-post election, where there is one and only one winner, quota is the well-known 50% + 1. Expressed mathematically, it’s (1⁄2*v + 1) where v is the total number of votes. A candidate with that many votes can’t be beaten by anyone else; there simply aren’t enough votes left. A candidate could be elected with fewer votes, but (1⁄2*v + 1) guarantees a win.
In a region where we elect two winners, quota is (1⁄3*v + 1). If candidates A and B both have just over 1⁄3 of the votes, no other candidate can obtain more than 1⁄3 to beat them.
Similarly, in an election with three winners, quota is (1⁄4*v + 1) and for four winners quota is (1⁄5*v + 1).
The general formula is $$\frac{1}{n+1} v + 1$$ where n is the number of people to be elected and v is the number of votes.
There are actually several different ways to calculate quota. This approach is known as Droop quota.