Sample Size calculator Formula:
   ss = Z² × P × (1 - P) / C²
Where:
   Z: Z value (1.96 for 95% confidence level, 2.58 for 99%)
   P: Choice percentage ( 0 - 100 )
   C: Confidence Interval ( 0 - 100 )

If population is small, the sample size need adjustment as follows, otherwise, just leave the population field empty:
   ss = ss / ( 1 + (ss - 1)/population)