Sample Size Calculator (one group versus population)

Dear all,

so far I couldn´t find a solution to calculate the required sample size for the following scenario:

Goal: Research continuous variables (cost perceptions) of a population through one sample group. --> means of one group need to be significant for the entire population.

Population: 7.500.000
Confidence Level: 95%
Confidence Interval: 3

Are there any information missing like power level and does anyone know how I can calculate the required sample size for this scenario? Especially through an online tool would be highly appreciated.

Thanks very much.

It sounds like you are asking for the sample size needed to get a 95% confidence interval for a population mean (calculated from from one sample) to be +/- 1.5 but it isn't clear to me. If so the missing information is the SD of the data.
Can you explain a little more please? kat