I think what you are asking is which do you measure the inside or the outside of the pipe. From your question there doesn't need to be an answer. Usually it is the inside measurement that is meant. The useful part of the pipe or how much it can carry.
Three 0.50 inch diameter pipes will fit into one 1.50 inch diameter pipe (hypothetically). The 0.50 inch diameters stack on top of each other until you have 1.50 inches!
1/2 inch + 2*thickness of the pipe.
this depends on the class of the pipe as the higher the class the thicker the pipe
40
Thread size refers to the diameter of a threaded rod or pipe. In the case of 0.125 Inch NPT thread, the 0.125 Inch refers to the nominal inside diameter of the pipe that the thread will fit into. This means that the thread is designed to fit a pipe with a 0.125 inch inside diameter.
One foot of 3 inch pipe will hold approximately 0.625 gallons of water.
The weight of the pipe will depend on its volume, The volume in turn, will depend oninner radius or diameter,outer radius or diameter,length.Only one of these is given.
If I remember correctly, the pipe size is the inside diameter, so it would depend on the thickness of the wall, as to what size it would fit into.
The maximum flow rate for a 1 inch diameter pipe is typically around 8-12 gallons per minute. To calculate the maximum volume, you would need to multiply the flow rate by the amount of time the water is flowing.
pi x (42 - 12 - 12)/4 x 1/144 x 65 = 4.963 ft3
To calculate the gallons per foot in a 40-inch diameter pipe, you first need to find the volume of one foot of the pipe. The formula for the volume of a cylinder is (V = \pi r^2 h). For a 40-inch diameter pipe, the radius is 20 inches (1.67 feet), and the height (length) is 1 foot. This gives a volume of approximately 17.7 cubic feet, which is equivalent to about 132 gallons. Thus, a 40-inch pipe contains approximately 132 gallons per foot.
Pipe threads are stated in terms of so many threads per inch. For instance, a bolt designated as 1/4-20 is a 1/4 inch diameter bolt with 20 threads per inch. Divide one inch by 20 to find the pitch distance.