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Sample size calculator

Find the survey sample size needed for a population, confidence level and margin of error.

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Enter Population size, Confidence level, Margin of error (%) and the Sample size calculator works out Required sample size straight away. For instance, with Population size = 10,000, Confidence level = 90% and Margin of error (%) = 5 it returns Required sample size = 264.

How to use it

  1. Enter your values: Population size, Confidence level, Margin of error (%).
  2. Read the result instantly: Required sample size.

Frequently asked questions

What does the Sample size calculator actually compute?

It takes Population size, Confidence level and Margin of error (%) and derives Required sample size from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

3 values: Population size, Confidence level and Margin of error (%). Nothing else is required — no account, no file upload.

Can you show a worked example?

With Population size = 10,000, Confidence level = 90% and Margin of error (%) = 5, the calculator returns Required sample size = 264. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Population size = 20,000, Confidence level = 95% and Margin of error (%) = 5.5 instead, Required sample size goes from 264 to 313 — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Confidence level” option should I choose?

You can pick between « 90% », « 95% » and « 99% ». Each one changes what the calculator works out, so switch and compare — the default is « 90% ».

What does it give for smaller values?

Scaled down to Population size = 5,000, Confidence level = 90% and Margin of error (%) = 4.5, Required sample size comes out at 314. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Summarising a dataset before drawing conclusions from it, checking whether a difference between two groups is real, and putting an interval around an estimate.

What is the most common mistake?

Reading a p-value as the probability that the hypothesis is wrong. It is the probability of seeing data at least this extreme if the null were true — a different statement, and a much weaker one.

What is the difference between the Sample size calculator and the Sample Mean Calculator?

This one returns Required sample size; the Sample Mean Calculator returns Result. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Sample Standard Deviation Calculator is the closest one after this: Compute the sample standard deviation (n−1), variance, mean and detect outliers.

Further reading

All guides →
How-toHow to Calculate Standard Deviation (Step by Step)Standard deviation measures how spread out your data is. Here's the formula, a worked example, and the difference between population and sample.ExplainerA 1 % Drop Rate Does Not Mean One Hundred RunsAt 1 %, a hundred attempts give you 63.4 % — not certainty. Ninety per cent takes 230 attempts and ninety-nine takes 459, and more than a third of players are still empty-handed at a hundred.ExplainerWhat Is a Z-Score? Standard Deviations Above the MeanA z-score is z = (x − μ) / σ — how many standard deviations a value sits from the mean. Learn how to compute it, read the standard normal curve, and turn it into a percentile.ExplainerMean, Median and Mode: What's the Difference?Mean, median and mode all describe the 'middle' of your data — but answer different questions. Here's what each means, with examples and when to use which.ExplainerGeometric vs Arithmetic Mean: Which to UseThe arithmetic mean adds and divides; the geometric mean multiplies and takes a root. Learn which fits growth rates, ratios, and averages.ExplainerProbability Basics, With ExamplesProbability measures how likely something is, from 0 to 1. Here's the basic idea, how to combine events with AND and OR, and the complement.