Sample Size Calculator - Proportions/Percentages

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

Step 2:
Desired margin of error:   ± %

Step 3:
Estimated proportion (use 50% if unknown): %

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

Proportions/Percentage 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 = p(1-p)    p = estimated proportion

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 = p(1-p)    p = estimated proportion

e = desired margin of error

N = population size