Here is a standard method for figuring out how many votes you need to win:
1. How many registered voters are in your voting jurisdiction?
2. How many of these registered voters are likely to vote at the election your ballot question will be voted on? Look at similar elections in the past to gauge turnout, e.g., Primary or General Election, even (2014) or odd (2015) election year.
3. Of the LIKELY voters, you need a majority (50% + 1) to win. (NOTE: some jurisdictions, like the State of California, require a super majority to pass a funding measure. This must be taken into account when figuring out how many votes you need to win.)
4. Take the number of ”yes” votes needed and add a buffer to your goal in case turnout is higher than previous similar elections.