Required survey sample size for a target confidence level and margin of error.
A higher confidence level (e.g. 99% vs 90%) uses a larger z-score, which widens the formula's numerator and pushes the required sample size up — you need more responses to be more certain the true value falls within your margin of error.
Leave it at 50%. That's the most conservative assumption — it maximizes p(1−p) in the formula and gives the largest (safest) required sample size when the real proportion is unknown.
Only when you're sampling from a known, finite group (e.g. 500 employees in one company). The calculator then applies the finite population correction, which lowers the required sample size since you can't sample more people than exist. Leave it blank for large or unknown populations.