Less than an inch.
The answer depends on what the "36 inch" measures: inside circumference, radius, diameter?
10.4448, assuming 16" inside diameter. 16" outside diameter would be slightly less.
Pipe with a Nominal Bore of 4 inch (100mm) Outside Diameter 114.3mm
The circumference of a six-inch diameter circle is: 18.8 inches.
diameter = circumference/pi
Three-quarter inch diameter pipe refers to the outside diameter. Different pipe types of the same outside diameter usually have different inside diameters. ASTM SCH 40 pipe of 3/4 inch diameter has an inside diameter of 0.824 inches. ASTM CL 200 pipe of 3/4 inch diameter has an inside diameter of 0.930 inches because of the thinner wall.
The answer depends on what the "36 inch" measures: inside circumference, radius, diameter?
Then the wall thickness is 1 inch
The inside diameter (ID) is 8 inches. The nominal pipe size (NPS) and outside diameter (OD) depend on the thickness of the walls of the pipe.
10.4448, assuming 16" inside diameter. 16" outside diameter would be slightly less.
The pipe will have an outside diameter of 1.5+.25+.25 = 2". A pipe with an outside diameter of 2" has an outside circumference of 2"*Pi. 2"*3.142 ~= 6.284" or about 6 1/4"
Assuming that the 14 inch box is square, you could fit a circle inside with a 14 inch diameter.
Copper Tubing Size, Outside Diameter controlled. - How copper and PEX tubing size is specified based on the outside diameter. Common sizes are 3/8, 1/2, and 3/4 inch. This contrasts to pipe sizing which is based on the inside diameter.
1/12th inside diameter plus 1 inch for 'B' wall (most common type), additionally, pipe sizes are normally in 1/4 or 1/2 foot increments, so the closest size would be a 24 inch diameter with 3 inch wall (24/12=2+1=3) having a outside barrel diameter thickness of 30 inches for 'A' wall 1/12th inside diameter, 'C' wall is 1/12th inside diameter plus 1 3/4 inch
0.3344 square inch
8 "
The outside diameter of a 1/2 inch PVC pipe is approximately 0.840 inches.