15x20 Pergolas

15x20 Refers to the Combined Inner Dimensions of the 4 Roof Openings

When we say a pergola's dimensions are 15x20, we are referring to the combined inside dimensions of the 4 roof openings (from inside-edge to inside-edge). All of the kits featured on this page are meant to have 4 roof openings, arranged in a 2x2 grid, which combine to be a total of 15' wide and a total of 20' deep.

The overall outside-edge to outside-edge dimensions of the pergola will be:

• 16' 2.6" wide x 21' 2.6" deep (if you choose a kit for 4x4 posts) OR
• 16' 10.6" wide x 21' 10.6" deep (if you choose a kit for 6x6 posts)

With all of this being said, you can easily change the overall size of your pergola by trimming the wood posts that you plan to use for the roof beams. For example, if you wanted the true outside-edge to outside-edge dimensions of a free-standing pergola to be exactly 15' x 20', you would need to:

• Purchase three sets of two posts totaling 15 feet to be the beams running the 15-foot width, and then cut off a total of 14.6 inches (for 4x4 wood posts) or 22.6 inches (for 6x6 wood posts) per set of two posts; and
• Purchase three sets of two posts totaling 20 feet to be the beams running the 20-foot depth, and then cut off a total of 14.6 inches (for 4x4 wood posts) or 22.6 inches (for 6x6 wood posts) per set of two posts

Reminder: Width & Depth Are Not Always Interchangeable

15' x 20' pergolas are different from 20' x 15' pergolas. The wall-mounted pergolas on this page will attach to your home on the 15' width side and come 20' out from the house wall. For free-standing pergolas with a slatted roof, the roof rafters will be mounted to the 20' beams and run the 15-foot width of the pergola (providing more shade when the afternoon/evening sunlight comes from the 15-foot width side). If your afternoon/evening sunlight will come from the 20-foot side, you'll want a 20x15 pergola instead.