How do you calculate sample size for a survey?

A common approach uses n0 = (z^2 × p(1−p)) / e^2, then applies finite population correction if a population size is known: n = n0 / (1 + (n0−1)/N).

What should I use for p if I don’t know it?

If you don’t know p, using 0.5 is a common conservative choice because it yields the largest required sample size.

What confidence level and margin of error should I choose?

Common defaults for general surveys are 95% confidence and ±5% margin of error, adjusted based on how precise results need to be.

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Sample Size Calculator

Calculate how many completed responses you need for a target confidence level and margin of error. Then build your survey and start collecting in VividSurvey.

Finite population option
Conservative p = 0.50 default
Clear next steps

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Quick example

95% ±5%

With p = 50% and large population, sample size is about 385.

Confidence

95%

Error

±5%

385

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Use the calculator, then set a target responses goal and share your survey link.

CALCULATOR

Calculate recommended sample size

Uses a standard proportion sample size approach with optional finite population correction.

Confidence level

Common default: 95%.

Margin of error (±%)

Example: 5 means ±5%.

Expected proportion (p)

Use 0.50 for planning.

Population size (optional)

If provided, finite population correction is applied.

Create a survey to reach this sample size Calculate margin of error

What sample size means

Sample size is how many completed responses you need to estimate a percentage with a chosen confidence level and margin of error. A common approach first computes n0 = (z² × p(1−p)) / e², then applies finite population correction for smaller known populations: n = n0 / (1 + (n0−1)/N).

Why p = 0.5

When p is unknown, 0.5 is a conservative default that produces the largest required sample size for the same confidence and margin of error.

Practical next step

Use your expected response rate to estimate how many invites you need, then build and share your survey.

Create a survey and start collecting

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Want to learn more about sample size?

Read our comprehensive guide on sample size planning, confidence levels, margin of error, and how to plan invites based on response rate.

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