Well, the other day I was out buying myself one of those rolling portable waste tanks (saves on loading and unloading the camper just to go to the dump station), and I was trying to figure out how big of capacity my holding tank was.
Well, while I was at the RV Parts Outlet store in Tualatin, I made mention I had no clue what my tank's capacity was. The shop owner then replied, "Do you have a general idea of what the Length, width, and height of the tank is?"
I replied I had a ballpark figure. To which he gave me this formula.
(Length (In inches) x Width (In inches) x Height (in inches)) / 231 = approximate gallon capacity.
Giving my ball park figure I came out to roughly 25 gallons. Bought the biggest tank they had on hand (11 gallon) and only had to fill it twice to dump the tank, so that formula works pretty darned good.
Just thought I'd pass it along to anyone who buys a camper, but can't find the tank capacity, but can get the measurements on their tank.