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Free sample size calculator for proportion-based studies and surveys. Select confidence level, margin of error, estimated proportion, and optional population size to get recommended sample counts instantly.
Last updated: April 20, 2026
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Use 50% when prior proportion is unknown (most conservative estimate).
Base sample size (n0)
385
Finite adjusted sample
370
Z-score
1.960
Margin (decimal)
0.0500
Interpretation
For population size 10,000, adjusted sample size is 370.
Formula used:
n0 = (Z² × p × (1 - p)) / e²
Finite correction: n = n0 / (1 + (n0 - 1)/N)
Core formula
n0 = (Z² × p × q) / e²
Available levels
80%, 85%, 90%, 95%, 99%
Adjustment
n = n0 / (1 + (n0 - 1)/N)
Confidence: 95%, Margin: 5%, Proportion: 50%, Population: 10,000
Base sample
385
Finite adjusted
370
The calculator estimates minimum sample size required for a target confidence level and margin of error under a proportion model. It uses z-scores and allows finite population correction when your full population size is known.
n0 = (Z² × p × (1 - p)) / e²n = n0 / (1 + (n0 - 1) / N)Use p = 0.5 when uncertain, because it maximizes variance and gives a conservative sample size.
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