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Sample Size Calculator

Calculate required sample size for surveys and experiments.

Calculator

Margin of Error (%)

Confidence Level

Population Size (leave blank = infinite)

Expected Response % (default 50)

Result

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How to Calculate Sample Size for a Survey

Sample size determines how many respondents you need to get statistically valid survey results. A larger sample gives more accurate results but costs more time and money. The key factors are: population size, confidence level (usually 95%), margin of error (usually ±5%), and expected response distribution.

Confidence Level	Z-Score	Margin of Error	Min Sample (large pop)
90%	1.645	±5%	271
95%	1.960	±5%	385
95%	1.960	±3%	1,068
99%	2.576	±5%	664
99%	2.576	±1%	16,590

Sample Size Formula

n = Z² × p(1−p) ÷ e², where Z = z-score for confidence level, p = expected proportion (use 0.5 for maximum sample), e = margin of error as decimal. For small populations, apply finite population correction: n_final = n ÷ (1 + (n−1)/N).

What sample size do I need for 95% confidence with ±5% margin?

For a large population (10,000+), you need a minimum of 385 respondents for 95% confidence level and ±5% margin of error, assuming 50% response distribution (most conservative).

Does population size affect sample size much?

For large populations (above 10,000), population size barely affects the required sample size. For small populations (below 1,000), the finite population correction reduces the required sample significantly.