Plan minimum survey sample size for a proportion: expected rate, margin of error, and confidence level (simple random sample, no finite correction).
How to use
- Enter expected proportion (0–1).
- Enter margin of error (0–1, e.g. ±5 points → 0.05).
- Pick confidence level and read the rounded-up minimum n.
Example
Unknown proportion → use 0.5 for a conservative plan; MOE 0.05 at 95% often lands in the mid hundreds (see live output).
Tighter MOE 0.03 needs a noticeably larger n.
Related: confidence interval, probability calculator.
Notes
Strata, non-response, and finite populations need extra allowance.
Frequently asked questions
Unknown proportion?
Use 0.5 for a conservative maximum n at a given margin.
What is margin of error 0.05?
0.05 means about ±5 percentage points at your confidence level; 0.03 is tighter and needs more people.
Why round sample size up?
You cannot survey a fraction of a person—results round up to the next whole respondent.
Vs confidence interval calculator?
CI page: interval from existing data. This page: plan how many to survey.
Strata or non-response?
This is a simple random-sample formula; strata and non-response usually need extra allowance.
Can I save my inputs?
Yes. Copy link below the form keeps your current inputs so you can share the scenario or save it for later.