How to calculate sample size

Variables in equation are.

s = Required Sample size
z = confidence level of 90% - 99%
p = Estimated proportion of respondents who will buy dog supplies over the Internet
c = confidence interval + or - 4% or + or - 5%

Sample size = Confidence Interval Squared Times Population Times 1-Population divided by Confidence Interval squared

s= z^2 * (p) * (1-p)/c^2

Plase click on the appropriate button to enter variables. Click Calculate button when finished.

Confidence level = 90% - 1.645
Confidence level = 95% - 1.96
Confidence level = 99% - 2.576

Level of precision = ± 4%
Level of precision = ± 5%

20% Estimate percentage who will buy our products over Internet
30% Estimate percentage who will buy our products over Internet
40% Estimate percentage who will buy our products over Internet
50% Estimate percentage who will buy our products over Internet