Select the stands you want calculated and then click on the 'Simple' button  which is located on the Dynamic ribbon (pic 1) or, if you want to calculate ALL stands, select the 'Simple' option from the 'Meterage Report' which is located on the HOME ribbon (pic 2)

NOTE: The Dynamic Ribbon will not appear if you have entities other than stands selected, to deselect the other entities and only select stands, press F3. Remember to press F3 again once finished so you can select other entities.