Statistics
Survey sample size calculator
Planning a survey or poll? Pick a confidence level and margin of error (and optionally a population size) to see how many responses you need.
- Recommended sample size
- 385
- responses needed for a 95% confidence level with a ±5% margin of error.
Uses the standard formula with the most conservative response split (50/50), which gives the largest — safest — sample size. Providing a population applies the finite-population correction, which lowers the number for smaller groups.
Confidence and margin of error, plainly
Two choices drive the sample size. The confidence level is how sure you want to be that the true value falls within your result’s range; the margin of error is how wide that range is. Wanting more confidence or a tighter margin both push the required sample up — and the relationship isn’t linear, which is why halving the margin roughly quadruples the sample.
Why samples can speak for millions
A well-drawn sample of a few hundred can represent a huge population — the logic behind population vs sample. To understand sampling, polls, and margins of error properly, explore the Statistics subject.
Frequently asked questions
- How many people do I need to survey?
- It depends on how confident you want to be and how precise the result should be. Choose a confidence level (commonly 95%) and a margin of error (commonly ±5%), and this tool gives the recommended number of responses — around 385 for a very large population at 95% and ±5%.
- What is the margin of error?
- The margin of error is how far your survey result might be from the true value, in percentage points. A ±5% margin means a measured 60% could really be anywhere from 55% to 65%. A smaller margin needs a larger sample.
- Why does the population size barely change the answer?
- For large populations, the required sample barely grows — surveying a whole country needs only a little more than surveying a large city. The population size only matters much when it’s relatively small, where the finite-population correction reduces the number needed.
- Is it free and private?
- Yes — nothing is stored and there’s no sign-up. It all runs in your browser.