What formula would I use to convert a pipe to cubic feet?
ex. i.d. 6" x 21' pipe, .28" thickness = how many cubic feet
Do you want the volume of the whole pipe (including inside air space) or just the volume of the metal?
If outside diameter, Do, is 6", the inside diameter, Di, is Do - 2*t, or 5.44".
We can't use mixed units, so converting length to inches, 21' x 12 in/ft = 252 in. Later, we will convert to cubic feet using 1728 in³/ft³
The volume of the whole pipe is (pi/4)*Do²*L
Excluding the inside of the pipe, the volume of metal is (pi/4)*(Do² - Di²)*L
The whole pipe is 7125 in³ or 4.12 ft³
The volume of metal in the pipe is 1268 in³ or 0.7338 ft³