The strain gauge measuring grid length depends on the aim of measurements, as the result of the measurement using strain gauges will be the mean strain underneath the measuring grid. In general, measuring grid lengths of 3 or 6 mm (0.118 or 0.236 inches) represent a good solution.
Long measuring grids are recommended where there is an inhomogeneous material, such as concrete or wood. A long strain gauge will bridge the inhomogeneities of the work piece and, as a measurement result, will supply the strain underneath the measuring grid.
Short measuring grids are suitable for detecting a state of local strain. They are therefore suitable for determining strain gradients, the maximum point of notch stresses and similar stresses.