Sample Size Calculator

Estimate how many observations are needed to measure a population proportion at a selected confidence level and margin of error.

What This Sample Size Calculator Calculates

Estimate how many observations are needed to measure a population proportion at a selected confidence level and margin of error. The calculation runs locally in your browser, so the values you enter are not sent to OfficeCalculator.Net by this tool.

Formula

n₀ = z²p(1−p) ÷ e²; finite population: n = n₀ ÷ [1 + (n₀−1)/N].

How to Use the Calculator

1. Enter the requested values using the same time period and units where applicable.
2. Review percentages, dates, or currency selections before calculating.
3. Select Calculate to generate the main result and supporting metrics.
4. Use Copy, Share, or Save Result Image when you need to keep the result.

Worked Example

Example: a population of 10,000, 95% confidence, 5% margin of error, and a 50% expected proportion produces a sample size using finite-population correction.

Common Uses

• Plan survey response targets.
• Estimate sample requirements for a proportion.
• Compare confidence-level and margin-of-error choices.

Important Notes

This calculator is designed for planning, comparison, and educational use. Results depend on the assumptions and values entered. Financial, payroll, statistical, and policy rules can vary by organization and location, so verify important decisions against the relevant records or professional requirements.

Frequently Asked Questions

Why is 50% often used for expected proportion?

When no prior estimate is available, 50% produces the largest variance and therefore a conservative sample-size estimate for this formula.

What does population size 0 mean?

It tells the calculator to use the large/unknown population formula without finite-population correction.

Does sample size guarantee representative results?

No. Sampling design, nonresponse, bias, and data quality also affect the usefulness of results.