Sample Size calculator - Means

Step 1:
Desired confidence level: 99%   95%   90%

Step 2:
Desired margin of error:   ±

Step 3:
Estimated standard deviation:

Step 4:
Population size: infinite   actual/estimated
  • use 'infinite' when the group is larger than 1, or you don't know the actual size of the overall population

    Required Sample Size:

 

see formula

Means Sample Size

Formula

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