Sample Size Calculator

Proportion Mean

Confidence Level (%)

Common choices are 90, 95, or 99.

Margin of Error (%)

How much error you can tolerate, e.g. 5 means ±5%.

Expected Proportion (%)

Your best guess of the true proportion. Leave blank to use 50% — the most conservative assumption, which gives the largest (safest) sample size.

Population Size (optional)

Only matters if your population is small relative to your sample.

About This Tool

How Many People Do I Need to Survey?

Sample size calculators tell you the minimum number of observations needed to estimate a population value within a chosen margin of error, at a chosen confidence level. Bigger samples give more precise estimates, but with diminishing returns.

When to Use It

Planning how many survey respondents you need for a given precision
Designing a study or experiment before collecting data
Justifying your sample size in a dissertation methodology section

The Formulas

\( n = \dfrac{Z^2 \cdot p(1-p)}{E^2} \) (proportion) \( n = \dfrac{Z^2 \sigma^2}{E^2} \) (mean)

Worked Example

You want to estimate what proportion of students prefer online learning, with 95% confidence and a margin of error of ±5%. You have no prior estimate, so you use the conservative 50%.

\( Z = 1.96, \ p = 0.5, \ E = 0.05 \)
\( n = 1.96^2 \times 0.5 \times 0.5 / 0.05^2 \approx 384.16 \)
Rounded up: you need at least 385 respondents — a widely cited benchmark for this exact scenario.

Your Results

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Sample Size Calculator

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