Sample Size: 90% Confidence, 5% Margin of Error
At 90% confidence and ±5% margin of error with p = 0.5, a sample size of 271 is sufficient.
How to use this tool
- Enter expected proportion (p), z* (confidence level) and margin of error (e) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your required sample size (n) and the full breakdown beneath it.
Find how many respondents you need for a 90% confidence survey with a 5% margin of error, a common choice for lower-stakes research.
Frequently asked questions
- Why use p = 0.5 when the proportion is unknown?
- p × (1−p) is maximised at p = 0.5, giving the most conservative (largest) required sample size. If you have a prior estimate of p, use it to get a smaller required n.