12x18 Pergolas

12x18 Refers to the Combined Inner Dimensions of the 2 Roof Openings

When we say a pergola's dimensions are 12x18, we are referring to the combined inside dimensions of the 2 roof openings (inside-edge to inside-edge). All of the kits featured on this page are meant to have 2 roof openings that are both 12' wide and which combine to be a total of 18' deep. (Note: If you choose a kit made for a slatted wood roof, the combined depth of the 2 roof openings can be divided any way you'd like: both 9' deep or one 9.5' and one 8.5' deep or one 10' and one 8' deep or any other combination that adds up to 18 feet.)

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

• 12' 7.3" wide x 19' 2.6" deep (if you choose a kit for 4x4 posts) OR
• 12' 11.3" wide x 19' 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 12' x 18', you would need to:

• Purchase three 12-foot posts to be the beams running the 12-foot width, and then cut off 7.3 inches (for 4x4 wood posts) or 11.3 inches (for 6x6 wood posts) from each one; and
• Purchase two sets of two posts totaling 18 feet to be the beams running the 18-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.

Important Note: Our shade canopies are specifically designed to fit roof openings that are exactly 8x8, 8x10, 8x12, 10x10, 10x12 and 12x12. If you're purchasing a kit with shade canopies, you cannot trim down the roof beam posts. Furthermore, all roof posts must be 8-, 10- or 12-foot lengths.

Reminder: Width & Depth Are Not Always Interchangeable

12' x 18' pergolas are different from 18' x 12' pergolas. The wall-mounted pergolas on this page will attach to your home on the 12' width side and come 18' out from the house wall. For free-standing pergolas with a slatted roof, the roof rafters will be mounted to the beams on the 18' side and run the 12-foot width of the pergola (providing more shade when the afternoon/evening sunlight comes from the 12-foot width side). If your afternoon/evening sunlight will come from the 18-foot side, you'll want an 18x12 pergola instead.