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Event survey sample size calculator
For 800 attendees you need 260 responses for a ±5-point margin at 95% confidence, a 33% response rate. At 30% you get 240 responses and about ±5.3 points. The formula is Cochran’s sample size with a finite-population correction; enter your audience, response rate and the groups you want to compare.
Responses needed
260
for ±5 points at 95% confidence from 800 people
You need a 33% response rate; at 30% you get ±5.3 points. Ask inside the app before people leave, keep it to five questions, or accept the wider margin.
- Response rate needed
- 33%you expect 30%
- Responses you can expect
- 240short
- Margin you will get
- ±5.3 pointswith 240 responses
| Responses needed (whole audience) | 260 |
|---|---|
| People to invite at your response ratemore than you have | 867 |
| Margin you will get | ±5.3 points |
Assumes respondents are like non-respondents. If only the happiest answer, a bigger sample does not fix the bias.
How we calculate
- Infinite-population size
n₀ = z² × p × (1 − p) ÷ e²z = 1.645, 1.96 or 2.576 for 90%, 95% or 99% confidence; p = expected split; e = margin.
- Responses needed
n = n₀ ÷ (1 + (n₀ − 1) ÷ attendees), rounded upSmall audiences need fewer responses than the textbook 385.
- Margin you will get
z × √(p(1 − p) ÷ responses × (attendees − responses) ÷ (attendees − 1))With responses = attendees × your response rate.
- Per group
the same formula with attendees ÷ groupsComparing tracks or regions needs enough responses in each one.
Assumptions
- Simple random sample: the people who answer are like the people who do not. Response bias is not fixed by a bigger sample.
- A 50% expected split gives the largest (safest) sample size.
- In-app forms during the event often get 25–40% responses; emailed surveys a week later 10–15%. These are planning ranges, not measurements.
- Groups are assumed equal in size.
Prices as of 23 Oct 2026.
Worked examples
| Scenario | Result | In one line |
|---|---|---|
| Conference, 800 delegates | 260 Responses needed | Survey sample size: 800 attendees, 95% confidence, ±5 points. Need 260 responses (33%); at 30% response you get 240 and ±5.3 points. |
| Association meet, 2,500 delegates, 6 tracks | 334 Responses needed | Survey sample size: 2,500 attendees, 95% confidence, ±5 points. Need 334 responses (13%); at 25% response you get 625 and ±3.4 points. |
Example inputs are illustrative, not client data. Tap “Start from” above to load either one.
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Questions about this calculator
How many survey responses do I need from event attendees?
For ±5 points at 95% confidence: about 260 from 800 attendees, 334 from 2,500 and 370 from 10,000. Smaller audiences need a larger share of people to answer.
What is a good response rate for event feedback?
Feedback asked inside the app during or right after a session often gets 25–40%. Emailed surveys a week later usually get 10–15%. Ask before people leave.
Can I compare tracks or regions?
Only if each group has enough responses. Six tracks of 400 people at 25% response give about ±8.5 points each, so treat smaller differences between tracks as noise.
Does a bigger sample fix biased answers?
No. If only the happiest or angriest people answer, more of them does not help. Keep the form short and ask everyone at the same moment.