A test structure includes a first plurality of lines and a second plurality of lines intersecting the first plurality of lines. The first and second pluralities of lines defining a grid having openings. A method for determining grid dimensions includes providing a wafer having a test structure comprising a plurality of intersecting lines that define a grid having openings; illuminating at least a portion of the grid with a light source; measuring light reflected from the illuminated portion of the grid to generate a reflection profile; and determining a dimension of the grid based on the reflection profile. A metrology tool is adapted to receive a wafer having a test structure comprising a plurality of intersecting lines that define a grid having openings. The metrology tool includes a light source, a detector, and a data processing unit. The light source is adapted to illuminate at least a portion of the grid. The detector is adapted to measure light reflected from the illuminated portion of the grid to generate a reflection profile. The data processing unit is adapted to determine a dimension of the grid based on the reflection profile.