You will need
• measuring tape;
• - caliper;
• calculator;
• - a sheet of paper and a pencil.
Instruction
1
To measure the external diameter of the pipe small size, use measuring tools such as caliper. Open the jaws of the instrument to the solution it was more than a section of pipe. Attach the caliper to the pipe and squeeze the jaws of the instrument so that they tightly gripped pipe. On a measuring scale to determine what is the diameter measured pipe. Caliper ensures accuracy measurement of the diameter of pipe to tenths of a millimeter.
2
To measure the internal diameter of the pipe, use the upper jaws of the Vernier caliper. Insert the sponge into the tube, and push them to the sponge fits snugly against the opposite inner ends of the pipe. On measuring scale, determine the internal diameter of the pipe. Keep in mind that the standard caliper allows you to measure the pipe diameter up to 150 mm.
3
If you need to measure the diameter of the pipe, without having access to it to slice, use a construction tape measure or a string (depending on pipe size). Measure using threads or tape measure the length of the pipe circumference (girth). Then the calculation of the external diameter of the pipe by the formula:
D = L / p where L is the length of the circumference of the pipe, p = 3,14 (PI).
For example, if the circumference of 400 mm outer diameter pipe will be:

D = 400 / 3,14 = 127,4 mm.
4
The inner diameter of the pipe calculate by the formula:
D’ = D – 2 * t, where D is outer pipe diameter and t is wall thickness.
So, for the above example, when the thickness of pipe wall is 3 mm, the inner diameter of the pipe will be:

D’ = 127,4 – 2 * 3 = 121,4 mm.
5
If you have a piece of pipe with a known surface area and the length of the segment, the diameter of the calculate, using the formula for the area of the lateral surface of the cylinder:
D = p * N / S, where N is the length of the pipe, S is the surface area, p = 3,14.

D’ = D – 2 * t, where D is outer pipe diameter and t is the thickness of its walls.