Survey Sample Size: How Many Answers Are Enough?
Survey accuracy depends on sample size more than on population size. A few hundred well-chosen responses often beat thousands of biased ones.
What is the Survey Sample Size Calculator?
Enter population size, desired margin of error, and confidence level, and the tool estimates the sample size using the standard Cochran formula with a 50% proportion. This is a planning estimate; real surveys also need to consider response rates and sampling method.
How to use it
- Enter the population size.
- Enter the margin of error you can accept.
- Pick a confidence level and click Estimate Survey Sample.
Worked example
For a population of 10000, 5% margin, and 95% confidence, the estimate is about 370 respondents.
Why assume 50% for the proportion?
It gives the largest, safest sample size, since it maximises variation. If you know the true split, the needed sample shrinks.
Frequently asked questions
Does a bigger population need a much bigger sample?
Not much. Beyond a few thousand, population size barely changes the required sample.
What about people who do not reply?
Invite more than the target. If only half reply, you need to invite roughly twice the sample size.