manhole size and constructibility

I have a drainage system laid out which has quite a few manholes with multiple pipes coming in at various angles. I am looking to get some suggestions/recommendations on how to use the available tools to make determination how big a manhole needs to be based on the pipes coming in.


Typically, we try to have at least 6 inches of concrete in the inside wall of the manhole between pipe OD+2" coring. I have approximately 50 manholes like this. Is there any easy way to figure out based on incoming pipe angles, pipe dia and material (thickness) that I can make a determination on the manhole size?


I am interested to know how everyone is doing this? I appreciate any help on this.