# Chi Square Sample Size Needed with G*Power

I was recommended to try G*Power so I could determine the sample size needed in order to achieve an acceptable power. I'm struggling with picking the test and filling out the appropriate values.

Basically, I'm sending a survey to approximately 3,000 people and am testing different times/days for response rate. So, for example, I'd like to send out on Monday, Wednesday, Friday, and Sunday, in the early morning, afternoon, evening, and middle of the night. So a total of 16 groups (4 x 4 conditions). This would give me 187.5 people in each group. Can anyone explain how I use G*Power or other software to figure this out?

When I select $X^2$ (chi-square) and goodness-of-fit and then "A priori" to calculate the required sample size, it asks me to determine p(H1) for each group, and I really don't know what to expect groups to achieve in terms of response rate. Furthermore, is a chi-square the right test, or should I be using an ANOVA (I am under the impression that ANOVA is for continuous variables, and I'd have a proportion)?