Space utilization uses the average row size and number of rows to compute the expected minimum size of leaf-level index pages and compares it to the current number of leaf pages.
If space utilization is low, running reorg rebuild on index or dropping and re-creating the index can reduce the amount of empty space on index pages, and the number of empty pages in extents allocated to the index.
If you are using space management properties such as fillfactor or reservepagegap, the empty space that is left for additional rows on leaf pages, and the number of empty pages left in extents for the index affects space utilization.
If statistics have not been updated recently and the average row size has changed or the number of rows and pages are inaccurate, space utilization may report values greater than 1.0.
