Sample Size Calculator
Calculate the minimum sample size required for a statistically valid survey or experiment. Specify confidence level, margin of error, and population size.
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How to use this calculator
n is the infinite-population sample size. n_adj applies a finite population correction when population size N is known.
- 1
Select your target confidence level (95% is the research standard).
- 2
Enter the acceptable margin of error — 5% is typical for surveys.
- 3
Leave response distribution at 50% if unknown (most conservative estimate).
- 4
Enter the population size if finite, or leave 0 for a large/unknown population.
Frequently asked questions
Why 50% response distribution?
p = 50% (0.5) gives the largest possible sample size because p(1−p) is maximised at 0.5. Using 50% is conservative and safe when you don't know the true proportion.
What is the finite population correction?
When your sample represents a large fraction of the total population, you need fewer responses than the infinite-population formula suggests. The finite correction reduces the required sample size.
Does a larger population require a larger sample?
No — once the population exceeds about 20,000, the required sample size barely changes. The margin of error is driven by the sample size, not the population fraction.
Sample Size Calculator — Survey & Research Planning
How sample size affects accuracy
A larger sample gives a narrower margin of error and more reliable results, but the relationship is not linear. Doubling your sample size cuts the margin of error by only √2 ≈ 41%. Going from 384 to 1,537 respondents takes you from ±5% to ±2.5% at 95% confidence.
Choosing the right confidence level
95% confidence is the standard in most research and surveys. 99% confidence is used in medical and safety-critical studies where the cost of a wrong conclusion is high. 90% is acceptable for exploratory research or when resources are limited.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →