The distance between two existing structures (2 gate posts, house, building, column, wall). ALL gate widths listed on our website equal the opening measurement… i.e. all gates listed on our website include the spacing needed for hinges. So, a 20 foot wide Industrial Driveway Gate will fit into a 20 foot wide opening, from post to post. The 2 gate-leafs that make up a 20 foot wide Industrial Driveway Gate will actually be less than 10 feet each because we have to accommodate spacing for the hinges. Example: if you are using 2 pairs of our Heavy Duty Gate Hinges with a 20 foot wide Industrial Driveway Gate (common), then each gate-leaf would be approximately 9 feet, 8 inches wide (actual width) because we subtract around 4 inches from each gate-leaf specifically for the Heavy Duty Gate Hinge.