Sample size for a descriptive study of a continuous variable

Instructions: Enter parameters in the red cells. The answer will appear in blue below.

CL = % Confidence level (e.g. 95%)
W = Desired total width of confidence interval
S = Standard deviation of the variable

W/S =

Standard normal deviate for α = Zα =

Sample size = N = 4Zα2S2/W2 =

Reference: Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing clinical research : an epidemiologic approach. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2013. Appendix 6D, page 80.