I just recently came across this website and was hoping an intelligent mind could help me calculate the sample size required for a study.

The study is comparing BMI and proximity to fast-food outlets.

Specifically comparing those <1km to >1km

Expected BMI difference considered significant >5

Accepted Power = 0.8 or 0.9+

Accepted Type 1 error = 0.05

Population size = 1,200,000

Population BMI = 25

Anything else that I need to know to figure this problem out?

I've had a look at a number of online calculators and videos to no avail. Most of it passes straight over my head.

If someone could send me some links / forumulas, or point me in the right direction that would be much appreciated.

Thanks!