Free Survey Sample Size Calculator
Pick a confidence level and margin of error to see how many completed responses your survey needs, and how many people to invite.
- No sign-up
- Private, in your browser
- Unlimited use
Know your number. Now reach it.
Build the survey from a Tapzy template, share it by link or QR code, and watch responses count up towards the sample you need, with results as live charts.
- Ready-made templates you can edit
- Share by link or QR code
- Results as live charts, no spreadsheet
How the sample size is worked out.
The first formula gives the sample for a very large population. If you enter a population size, the second formula reduces it, because each answer covers more of a small group. The result is rounded up.
The margin of error and expected proportion are entered as percentages and turned into fractions in the formula.
A quick example
At 95% confidence (z = 1.96), a ±5% margin and a 50% proportion need 385 responses from a very large population, or 278 from a population of 1,000.
Keep in mind
- Assumes a simple random sample. It doesn’t correct for bias or for people who don’t respond.
- This is the number of completed responses, not the number of people to invite.
- Very small groups or proportions near 0% or 100% may need a different method.
Common sample sizes
Completed responses needed for a very large population, with a 50% expected proportion.
| Margin of error | 90% confidence | 95% confidence | 99% confidence |
|---|---|---|---|
| ±10% | 68 | 97 | 166 |
| ±5% | 271 | 385 | 664 |
| ±3% | 752 | 1,068 | 1,844 |
| ±1% | 6,766 | 9,604 | 16,590 |
Choosing your settings
- Start with 95% and ±5%.It’s the most common choice for customer and market surveys.
- Use 50% when unsure.It gives the largest, safest sample size for the margin you chose.
- Plan invitations separately.Divide by your expected response rate: 385 responses at a 25% rate means inviting about 1,540 people.
- Think about subgroups.If you’ll compare groups, such as regions, each group needs enough responses on its own.
Sample Size Calculator questions
How many survey responses do I need?
At 95% confidence with a ±5% margin of error, you need about 385 completed responses from a large population. For a population of 1,000, you need about 278.
Why use 50% as the expected proportion?
50% gives the largest sample size for a given margin of error, so it's the safe choice when you don't know how people will answer.
Is the sample size the number of people to invite?
No. It's the number of completed responses. To find how many to invite, divide it by your expected response rate, or enter the rate in the calculator.
What if I don't know my population size?
Leave it empty. The calculator then assumes a very large population, which gives a slightly larger and safer sample size.
What confidence level and margin of error should I use?
95% confidence with a ±5% margin is the most common choice for customer and market surveys. Use a smaller margin when small differences matter.
Is my data private?
Yes. The sample size is worked out in your browser. Nothing you type is sent to Tapzy's servers.
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