Question

how is the number of delegates from each state to a party's national convention determined?

Answer 1

Both the Democratic Party and the Republican Party usually modify their delegate selection rules between presidential elections, including how delegates are allocated to each state and territory.

Under the 2008 Democratic Party selection rules, adopted in 2006, delegates are selected under proportional representation, which requires a candidate have a minimum of 15% of a state's popular vote to receive delegates. In addition, the Democratic Party may reject any candidate under their bylaws. Each state publishes a Delegate Selection Plan that notes the mechanics of calculating the number of delegates per congressional district, and how votes are transferred from local conventions to the state and national convention.[3] For the 2012 Democratic primaries, the number of pledged delegates allocated to each of the 50 U.S. states and Washington, D.C. is based on two main factors: (1) the proportion of votes each state gave to the Democratic candidate in the last three presidential elections, and (2) the number of electoral votes each state has in the United States Electoral College. States who schedule their primary or caucus later in the primary season may also get additional bonus delegates.[4]

Answer 2

Wikipedia might help lol