Large (Infinite) Populations
n = (zs/e)2
where:
z =
2.576 for 99% level of confidence
1.96 for 95% level of confidence
1.645 for 90% level of confidence
s = estimated standard deviation
e = desired margin of error
Finite Populations
n = (N(zs/e)2)/(N-1+(zs/e)2)
where:
z =
2.576 for 99% level of confidence
1.96 for 95% level of confidence
1.645 for 90% level of confidence
s = estimated standard deviation
e = desired margin of error
N = population size