Calculating Outer Diameter of Pipe

Measure around the pipe. Divide by 3.14. Have a nice day.

In MOST CASES its the inner diameter that is the more important and should be calculated rather than worrying with the outer diameter anyway so whats the point???

The ID is always going to vary depending on the wall thickness of the pipe being used...

One does not really calculate the O.D.; Pressure and flow calculations depend on the I.D. instead. Once those calcs are done, you select from a table of standard pipe sizes one that has sufficient thickness to withstand the pressure, and I.D. equal to or greater than the prior calc.

My hydraulic systems salesman had a chart with pipe sizes compared to flowrates, very valuable in choosing fittings and pipe. Distance matters, too.

"Pipe" will always be the same OD for each size so it can be threaded for fittings. The ID varies according to "schedule" and determines the pressure the pipe can hold.

There is a maximum flow for fluids, and that has to be accounted for, too. For hydraulic fluid, I think it was fifteen feet per second.