This document specifies a method for determining the rebound number of an area of hardened concrete using a spring-driven hammer. NOTE 1 The rebound number determined by this method can be used to assess the uniformity of concrete in situ, to delineate zones or areas of poor quality or deteriorated concrete in structures. NOTE 2 The test method is not intended as an alternative for the compressive strength determination of concrete (EN 12390-3), but with suitable correlation, it can provide an estimate of in situ compressive strength. For the assessment of in situ compressive strength, see EN 13791. NOTE 3 The hammer can be used for comparative testing, referenced against a concrete with known strength or against a concrete which has been shown that it has come from a defined volume of concrete with a population verified as conforming to a particular strength class.