Getting old and can't remember the formula to cypher the cubic inches in 3 inch PVC pipe, or how much length does it take to contain 130 cubic inches? Also, how do you convert fluid ounces to cubic inches?

1 U S fluid ounce = 1.805 cubic inch nomimal 3 inch diameter (ID) = 88.71 cubic inches per foot....this not PVC

3 Inch PVC has an ID if 3.068" and a square inch area of 7.393" so it will take 17.58" inches of 3 inch PVC to contain 130 cubic inches.

I too am getting old and forgetful and it has been a long time since I had to do much math but _IF_ PVC ID is 3.068 wouldn't the formula be 3.068 X 3.1416=9.4248 square inch area? 130 cubes -:- 9.4248=13.7933 of 3" PVC pipe? That 130 cubic inches should hold 72.02 fluid ounces? I may be wrong, usually am.

Nope :no: Area of a circle is Pi x Radius Squared. Therefore ID of 3.068" does yield an area of 7.393" and it still takes 17.58" inches of 3 inch PVC to contain 130 cubic inches. Yup, 130 cubic inches should hold 72 fluid ounces more or less.

I have created 3 soap mold rectangle boxes, the size is 13.25 by 3.5 by 1.5 inches. I calculate that to be 69.5 cubic inches each or 208.4 combined. Now as stated above a cubic inch contains 1.8 fluid ounces, so the 3 molds would hold 115 fluid ounces, are my figures correct? If I round down to 110 fluid ounces, to make up for mis measurements and mold lining would this be correct?