Survey sample size calculator
Before you send that survey, know how many responses you actually need. This calculator applies the standard sample-size formula — population, confidence level and margin of error in, required responses out.
Runs entirely in your browser — real, deterministic math. Nothing is uploaded, stored or sent anywhere.
Your survey parameters
The formula assumes maximum variance (p = 0.5), which is the conservative — and honest — way to plan.
Confidence level
How sure you need to be that the result reflects the whole population.
Margin of error
How much sampling error you can tolerate around the result.
Standard textbook formula, computed locally — nothing is uploaded. Plan your target, then let ClientTell collect and analyse the responses for you.
At 95% confidence with a ±5% margin of error, you need 278 responses from a population of 1,000.
That's about 28% of your population — with response rates typically running 10–30%, plan to invite several times this many.
Population
1,000
people you could ask
Uncorrected sample
385
formula before finite-population fix
Realistic invite target
1,390
assuming ~20% response rate
Why sample size is the quiet killer of surveys
A survey with too few responses produces confident-looking averages that are pure noise. Sample size is the difference between decisions based on signal and decisions based on weather.
Confidence is not accuracy
95% confidence means the true value lies within your margin of error 95 times out of 100 — if you asked everyone. Undersized samples quietly break that promise.
The formula assumes the worst
This calculator uses the conservative p = 0.5 assumption — maximum variance — which is why the numbers look larger than rule-of-thumb tables. That is the honest way to plan.
Aim high, then close the loop
Treat the result as your target, not a minimum to squeak past. And pair every survey with open-ended questions — the words are what turn the percentages into decisions.
Want ClientTell to monitor response rates — and read every answer with AI analysis automatically?
This calculator gives you a snapshot. ClientTell keeps the number live, reads the feedback behind it, and alerts you the moment a customer starts to slip.