FACTBOX: Delegate counts for presidential candidates

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

Voters choose the delegates state by state.

While the "Super Tuesday" contests on February 5 did not clinch the nomination for any candidate, those who did well may be on the way to victory since half the Democratic delegates and more than 40 percent of the Republican delegates were chosen on that day.

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 (total needed for nomination 2,025)

- Barack Obama 861

- Hillary Clinton 855

REPUBLICANS (number needed for nomination 1,191)

- John McCain 721

- Mike Huckabee 195

- Ron Paul 14

HOW DELEGATES ARE AWARDED

Democrats distribute delegates in proportion to their vote 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 contests are winner-take-all when awarding delegates, meaning Tuesday's victories by Sen. John McCain give him a commanding lead.

In addition to those elected state by state, a certain number of delegates at the conventions are set aside to be members of Congress, elected state officers and other leading party officials.

These "super delegates" are not committed to a particular candidate and can back anyone they choose.

Source of Delegate Count: msnbc.com

(Compiled by JoAnne Allen and Deborah Charles)