What tool is commonly used to measure the diameter of a pipe?

The tool commonly used to measure the diameter of a pipe is a caliper. Calipers are designed specifically for measuring the outside and inside dimensions of objects with precision. They can measure both the internal diameter of a pipe (using the inside jaws) and the external diameter (using the outside jaws). This capability makes calipers a preferred choice for tasks that require accuracy in measurement, particularly in mechanical and plumbing applications.

While a micrometer is another precise measuring instrument, it is primarily used for smaller dimensions and is not as practical for larger diameters typical of pipes. A ruler can be used for measuring but lacks the precision and versatility needed for accurately measuring the diameters of cylindrical objects. A tape measure, though useful for larger lengths and dimensions, does not provide the same level of precision as a caliper for measuring the specific diameter of pipes.