FACTBOX: Delegate counts for presidential candidates

(Reuters) - Delegates at the national party conventions in August and September will select the Democratic and Republican candidates who will face off in the U.S. presidential election on November 4.

Most delegates are chosen by voters in state by state contests.

Sen. John McCain of Arizona won enough delegates to become the Republican nominee, while U.S. media projected Sen. Barack Obama of Illinois clinched the Democratic nomination on Tuesday as the primary election season came to a close.

The Democratic Party voted on Saturday to seat half of the disputed Michigan and Florida delegations, meaning 2,118 delegates were needed to clinch the nomination.

Here are the total number of delegates awarded so far in nominating contests to the leading candidates, as estimated by MSNBC. Other news organizations may have reached different estimates.

DEMOCRATS (number needed for nomination 2,118)

- Barack Obama 2122

- Hillary Clinton 1925

REPUBLICANS (number needed for nomination 1,191)

- John McCain 1,266

HOW DELEGATES ARE AWARDED

Democrats distribute delegates in proportion to candidates' votes statewide and in individual congressional districts. That means candidates can come away with big chunks of delegates even in states they lose.

In contrast, most Republican states award their delegates on a winner-take-all basis.

In addition to the delegates chosen state by state, a certain number of elected officials and leading party figures attend the conventions as delegates. These "superdelegates" are not committed to a particular candidate and can back anyone they choose.

The number of superdelegates fluctuates at times, if someone resigns or if a new official with superdelegate status is elected somewhere in the country.

(Compiled by Andy Sullivan in Washington; Editing by Eric Walsh)