How to measure steel elongation?

find it out .

It's measured in the lab after a pull test.

Steel elongation can be measure manually or using device called extentiometer.

To measure elongation of steel manually we must give 2 punch marks on the specimen with specified length (see standard/code such as ASTM, ASME etc for specimen shape and size) addressed L0. After a pull test (tension/tensile test) we measure the distance between that 2 punch marks and addressed L1. Thus, the elongation of the specimen in percentage is ((L1-L0)/L0) x 100%.

Measure elongation using extentiometer is lot more easier because we can directly read the result. But this method limited for small elongation measurement only.