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SigmaCalc
Work backward from the precision you want to the number of people you need to survey.
The variance term p(1−p) is largest when p = 0.5, so using 50% as your estimated proportion (when you have no prior information) gives the most conservative, largest required sample size — you'll never be caught short.
Cutting your margin of error in half roughly quadruples the required sample size, since sample size scales with the square of the margin of error — going from ±5% to ±1% precision is far more than 5× the work.
Required sample size
385
respondents needed
What you entered
Worst-case variance term
0.5 × (1 − 0.5)= 0.25Apply the sample size formula
n = z² × p(1−p) ÷ E² = 1.96² × 0.25 ÷ 0.05²= 385Round up to a whole number of respondents
⌈385⌉= 385Result
Required sample size: 385
To estimate a proportion within ±5 percentage points at 95% confidence, you need at least 385 respondents — using 50% as the estimate (as done here by default) gives the most conservative, largest required sample.