Survey Size Calculator
For a simple majority yes/no survey of a very large population, this tool finds the survey size, risk of failure, and minimum voter sentiment required to pass.
See Random-Sample Voting for the motivation behind the calculator. See Surveying for a Voter Proposition to read about the underlying mathematics. See Computing Survey Size to read about the computational method. The calculation of the survey size is still a work in progress. No input for a Bayesian prior is included in the calculation, since taking the prior into account is trivial.