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Sample Size Calculator

Enter the total population size
Select your desired confidence level
Enter the margin of error percentage
Use 50% for a conservative estimate if unsure

Method and Reference

Methodology

This calculator uses Cochran's formula for sample size calculation, which is widely recognized in statistical research. The formula is:

n = (Z² × p × q) / e²

where:

  • n = sample size
  • Z = Z-score (based on confidence level)
  • p = population proportion (response distribution)
  • q = 1 - p
  • e = margin of error

For finite populations, we apply the finite population correction:

nadjusted = n / (1 + (n - 1) / N)

where N is the population size

References
  1. Cochran, W. G. (1977). Sampling Techniques (3rd ed.). New York: John Wiley & Sons.
  2. Bartlett, J. E., Kotrlik, J. W., & Higgins, C. C. (2001). Organizational Research: Determining Appropriate Sample Size in Survey Research. Information Technology, Learning, and Performance Journal, 19(1), 43-50.
  3. Krejcie, R. V., & Morgan, D. W. (1970). Determining Sample Size for Research Activities. Educational and Psychological Measurement, 30(3), 607-610.
Notes
  • The calculator uses a conservative approach by defaulting to 50% response distribution when unsure.
  • For populations under 100, the calculator will suggest a census approach.
  • The margin of error should be between 1% and 10% for practical applications.
  • Higher confidence levels require larger sample sizes.