Sample Size for Proportion Calculator
Enter an estimated proportion, a desired margin of error and a confidence level to get the minimum sample size needed to estimate a proportion at that precision.
What this calculator does
The Sample Size for Proportion Calculator estimates your result instantly from the values you enter, using standard statistics formulas. Enter an estimated proportion, a desired margin of error and a confidence level to get the minimum sample size needed to estimate a proportion at that precision. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Sample Size for Proportion Calculator
This calculator finds the minimum sample size needed to estimate a population proportion. Enter your best estimate of the proportion, the margin of error you can tolerate and a confidence level (90%, 95% or 99%), and it returns how many respondents you need.
Use it when planning a survey or poll and you want a target proportion known within a set precision. The result is always rounded up to a whole number of respondents.
Formula & Mathematical Calculation
Required Sample Size = f(Estimated proportion (0–1), Desired margin of error, Confidence level)
Calculated according to standard stats formulas implemented in the calculator core.
Calculation Example
Enter an Estimated proportion of 0.5, a Desired margin of error of 0.05, and select the 95% confidence level, then click Calculate.
The tool returns Required Sample Size = 385, with the note: “You need at least 385 respondents to estimate the proportion within ± 5%.”
Key Benefits
- Returns the minimum number of respondents needed for a target proportion and precision
- Offers 90%, 95% and 99% confidence levels through a simple dropdown
- Always rounds the required sample size up to a whole number of people
- Restates the margin of error as a percentage in the result note
How to Use this Calculator
-
Enter the estimated proportion
Type your best estimate of the proportion as a decimal between 0 and 1; use 0.5 if you are unsure, as that needs the largest sample. -
Enter the margin of error
Type the precision you want as a decimal, for example 0.05 for plus or minus 5 percent. -
Choose the confidence level
Select 90%, 95% or 99% from the confidence level dropdown. -
Calculate
Click Calculate to read the Required Sample Size box and the note explaining the margin of error.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Sample Size for Proportion Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.