How to Measure Patio Umbrellas:  Patio Umbrella Size is determined in width “not” height.  To find the correct measurements, measure the distance between the top of the rib arm and the bottom the rib arm.  Then simply multiply that by two, which will give you the correct size.
IMPORTANT NOTE: There are hundreds of umbrella manufacturers all over the world.  Most umbrella manufacturers build individual umbrellas to their own specifications, meaning that all umbrellas are not created equal and or built to the same length, diameter and thickness. 

“Most Patio umbrellas will very in width up to several inches depending on each manufacturer”.    

 Example:  A true 9’ umbrella span would be 108 inches (12” x 9” = 109”).  However, particular rib arms may be up to several inches longer or shorter, causing the over all umbrella span to be greater or smaller then 109” actual inches.