# Calculating required sample size

I am currently using a formula I got from a Qualtrics blog post to calculate the sample I require for a survey for the mean to be meaningful/reflect the population mean, as follows:

http://imgur.com/a/YKzBH

My survey has a large Std.dev (1.8), which I use instead of assuming a 0.5 Std.dev. This formula does not seem to take into consideration the population size (>10 000), however.

Is there an alternate formula to calculate required sample size with a known population size (but an unknown population std.dev)?

Population size is irrelevant unless the sample is a large portion of the population, which is clearly not the case here. There is a finite population correction: $FPC = \sqrt{\frac{N-n}{N-1}}$