Looking for caculator for bulkhead size

[allincuddy]

I had one on some place on the internet, punch in the size of bulkhead and it would tell you how many gallons (capacity) it would do. Now I must have deleted it and need to do a calculation.
I have a 7/8" ID on a 65 and wondered if that would give me 3 turn overs or 195 gal. per hour??
If anyone can help, I would appreciate it.
Thanks.