Sample Size Calculator

Sample size is the number of observations needed to estimate a population parameter within a specified margin of error at a given confidence level. Larger samples give more precise estimates, but the relationship is not linear — quadrupling the sample only halves the margin of error.

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1. 1Determine your confidence level (usually 95%) and margin of error (usually ±5%)
2. 2Estimate the proportion p (use 50% if unknown — gives the most conservative/largest sample)
3. 3Formula: n = z²×p×(1−p) / e²
4. 4For finite populations, apply correction: n_adjusted = n / (1 + (n−1)/N)