Proportion Sample Size Calculator
Plan a sample size for a normal-approximation proportion margin of error.
Your result
MATHEnter your values and select calculate.
On this page How it works & practical examples
How to use the Proportion Sample Size Calculator
Express the margin as absolute percentage points, not as a relative percentage of the proportion. Use 50% when seeking the largest size under this basic variance model.
The calculation
Worked example
A 50% planning proportion, five-percentage-point margin and z = 1.96 require 385 observations.
Assumptions and limits
Assumes independent simple random sampling and an effectively large population. This is a planning approximation; nonresponse, design effects and subgroup analyses can require more observations.
Common questions
Which inputs should I use?
Express the margin as absolute percentage points, not as a relative percentage of the proportion. Use 50% when seeking the largest size under this basic variance model.
What does the result exclude?
Assumes independent simple random sampling and an effectively large population. This is a planning approximation; nonresponse, design effects and subgroup analyses can require more observations.