To provide a pipe ruler having excellent work efficiency, capable of executing accurate measurement, and being applied to pipes having various sizes from a large caliber to a small caliber without requiring measurement by taking troublesome procedures such as a leveling string or the like, or requiring a troublesome work on the field by using a large-sized device.

This pipe ruler has a ruler body having a prescribed length on which a guide capable of measuring the size along the longitudinal direction is formed, and a pair of right and left support arms provided with a fulcrum on the lower part of the ruler body, and a support part loadable on the outer circumference of a pipe or rounded articles by forming bent parts on the intermediate part, and equipped with a slide part installed on the upper part slidably along the longitudinal direction of the ruler body. The pipe ruler is characterized by enabling to cope freely with pipe diameters by adjusting the height of the slide part installed on the pair of right and left support arms corresponding to the pipe diameter of the pipe or the rounded articles and by narrowing or widening the interval of the intermediate support part.