How to Calculate Sample Size Calculator
What is 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.
Step-by-Step Guide
- 1Determine your confidence level (usually 95%) and margin of error (usually ±5%)
- 2Estimate the proportion p (use 50% if unknown — gives the most conservative/largest sample)
- 3Formula: n = z²×p×(1−p) / e²
- 4For finite populations, apply correction: n_adjusted = n / (1 + (n−1)/N)
Worked Examples
Input
95% CI, ±5% margin, unknown proportion
Result
n = 385
The standard "385 rule" for large populations
Input
99% CI, ±3% margin
Result
n = 1,844
Higher confidence and precision requires much larger sample