Sample size calculation

I have a normal distribution:

log(xi/yi) ~N (0, c^2/yi).

I need to work on the posterior distribution of c^2.

I know c^2 follows a gamma distribution. I need to know what sample size I need to estimate the c^2?


Ambassador to the humans
Your question isn't very clear to me. Are you working in a bayesian setting? Can you provide more background on what your quantities/parameters are here?