📊 Statistics

Sample Size Calculator

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

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Results

Required sample size
385

📊 Sample Size Calculator chart

How the required sample size changes as the margin of error varies. The orange dot marks your current value.

What is the Sample Size Calculator?

Find the survey sample size needed for a confidence level and margin of error. Paste a list of numbers from any spreadsheet or document and get descriptive statistics instantly. Each statistics calculator also charts your data so outliers stand out.

Sample Size Calculator – free online statistics tool illustration
Sample Size Calculator — free, exact and private.

How to use the Sample Size Calculator

  1. Enter your confidence level, your margin of error, your population size, your expected proportion.
  2. Results update automatically as you type; you can also press Calculate.
  3. Read the output: required sample size.
  4. Use the 📊 chart to see the result visually, then copy or share it.

Formula and method

n₀ = z² p(1 − p) ÷ e²; finite: n = n₀ ÷ (1 + (n₀ − 1)/N)

Worked example

With confidence level = 95%, margin of error = 5 %, population size = 0, expected proportion = 50 %, the Sample Size Calculator returns required sample size: 385.

Tips for better results

  • Use sample standard deviation (n − 1) for samples and population (n) for complete data sets.
  • Check the chart for outliers before trusting a mean.
  • Quartiles here use the inclusive interpolation method, matching Excel’s QUARTILE.INC.

Frequently asked questions

What does the Sample Size Calculator do?

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

How is it calculated?

The Sample Size Calculator uses this method: n₀ = z² p(1 − p) ÷ e²; finite: n = n₀ ÷ (1 + (n₀ − 1)/N).

Can you show an example?

With confidence level = 95%, margin of error = 5 %, population size = 0, expected proportion = 50 %, the Sample Size Calculator returns required sample size: 385.

Is the Sample Size Calculator accurate?

Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.

Is this tool free and private?

Yes — the Sample Size Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.

Related tools

Margin of Error CalculatorCalculate the margin of error for a survey or poll.Average CalculatorCalculate the average (arithmetic mean), sum and count of a list of numbers.Mean, Median, Mode CalculatorCalculate mean, median, mode and range of a data set at once.Median CalculatorFind the median (middle value) of a list of numbers.Mode CalculatorFind the mode — the most frequent value(s) — in a data set.Range CalculatorFind the range, minimum and maximum of a data set.Standard Deviation CalculatorCalculate sample and population standard deviation and variance.Variance CalculatorCalculate the sample and population variance of a data set.

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