What sample size do I need for a 95% confidence interval?

For 95% confidence with ±5% margin of error and unknown population: n = (1.96² × 0.5 × 0.5) / 0.05² = 385 people. This is the most common research standard.

How does population size affect sample size?

For large populations (>100,000), population size barely affects the required sample. For small populations, use the finite population correction which reduces the needed sample.

Sample Size Calculator

Quick answer: Enter confidence level and margin of error to get the minimum sample size for a statistically valid study.

Determine how many participants you need for your survey or study to achieve statistically valid results. Enter your confidence level and margin of error to get the required sample size.

Last reviewed: April 2026Report an error

Confidence Level

Margin of Error

Population (optional)

Required Sample Size

385

Required sample size: 385 at 95% confidence.

Required Sample Size

385

How to Use This Sample Size Calculator

1Select your confidence level (90%, 95%, or 99%).
2Enter your acceptable margin of error as a decimal (e.g., 0.05 for ±5%).
3Optionally enter population size for finite population correction.
4Read the required sample size.

Frequently Asked Questions

: For 95% confidence with ±5% margin of error and unknown population: n = (1.96² × 0.5 × 0.5) / 0.05² = 385 people. This is the most common research standard.
: For large populations (>100,000), population size barely affects the required sample. For small populations, use the finite population correction which reduces the needed sample.

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Sample Size Calculator

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