How to use the Sample Size Calculator
Estimate required sample size from confidence level, expected proportion, target margin of error with the Sample Size Calculator. It includes Required sample size, Achieved precision workflows, so choose the one that matches the values you actually know. Use it to check the arithmetic while keeping the displayed method and entered values with your work.
Step by step
- For the Sample Size example, select Required sample size and enter confidence level, expected proportion, target margin of error, population size. Keep each value in the unit displayed beside its field.
- Review the selected Sample Size workflow and inputs, then read required sample size in the result panel.
- Change one Sample Size assumption at a time to compare scenarios. Use Reset to restore this tool's worked example values.
How the calculation works
Plans a proportion sample from confidence and precision, applies finite-population correction when a population is supplied, and can reverse the formula to show achieved margin.
Worked example
To reproduce the Sample Size worked example, reset the calculator. Select the Required sample size workflow. Use confidence level 95 %; expected proportion 0.5; target margin of error 0.05; population size 0. The result is required sample size of 385. Required sample size: Plans a proportion sample from confidence and precision, applies finite-population correction when a population is supplied, and can reverse the formula to show achieved margin. Review the displayed units before comparing the result.
Understanding the result
The Sample Size reports required sample size. Use it to check the arithmetic while keeping the displayed method and entered values with your work. The result depends on the entered values, selected mode, and displayed mathematical assumptions.
How to check the answer
Check the Sample Size answer by substituting required sample size back into the stated relationship. Test a simple value such as zero, one, or an equal pair, then confirm that sign, scale, units, and rounding match Plans a proportion sample from confidence and precision, applies finite-population correction when a population is supplied, and can reverse the formula to show achieved margin.
Common questions
What does the Sample Size calculate?
Estimate required sample size from confidence level, expected proportion, target margin of error with the Sample Size Calculator.
Which inputs does the Sample Size example use?
The worked example uses confidence level, expected proportion, target margin of error, population size in the Required sample size workflow. Other workflows can show different fields. Keep the chosen workflow and units with the result when comparing calculations.
Is the Sample Size result exact?
The result depends on the entered values, selected mode, and displayed mathematical assumptions. Recheck confidence level, expected proportion, target margin of error and use required sample size only for a decision where that level of precision is appropriate.