You are asking how to "calculate" post reward(s?) in steemit. I assume you are asking how one single post gets it's rewards based on the votes from other Steemians.
TL;DR - there's no point. There is too much variable in place that it's humanly immposible to calculate them, just leave it to the blockchain to do it for you..
But.... If you insist, @themarkymark made a very technical post about it more than half a year ago here at https://steemit.com/steemit/@themarkymark/how-to-calculate-post-rewards