In counting votes for electing candidates under a

**single transferable vote**
electoral system, the
minimum number of votes needed for a candidate to be elected (the
quota) can be calculated by using the Droop quota
formula. The quota is calculated as follows: first, the
total valid vote in the electoral district is divided by one plus
the number of members to be elected; then, one is added to the
total (fractions are ignored).

The Droop quota is the smallest number of votes to
elect enough candidates to fill all the seats being contested in an
electoral district, while being just big enough to prevent any more
being elected. If the Droop formula is applied to a
single member district, the quota is the total votes (100 percent)
divided by 1 plus the number of members to be elected (1); the
result is 100 divided by 2 which gives 50 percent plus one
vote—a share of the vote that only one candidate can
get.

H R Droop was an English lawyer who suggested this
formula in 1868 as a component of an electoral system.