Pergola Calculator
A pergola transforms a plain patio into an outdoor living space, but a trip back to the lumber yard mid-build is no fun. This calculator figures out every piece of lumber you need -- posts, doubled beams, rafters, and optional cross pieces for extra shade. Enter your dimensions and spacing preferences, and you get exact counts plus total board feet for ordering.
Pergola Components
A standard pergola has four main structural elements:
- Posts -- Vertical supports, typically 6x6 for spans over 8 feet or 4x4 for smaller pergolas. Set in concrete footings or mounted on post bases.
- Beams -- Horizontal members running the length of the pergola, bolted to the posts. Usually doubled (sandwiched around the post) for strength and aesthetics.
- Rafters -- Span across the width, sitting on top of the beams. Spaced 12-24 inches apart. These are the most visible structural element.
- Cross pieces -- Optional smaller members running perpendicular to rafters. They add visual detail and increased shade.
Lumber Sizing Guide
| Span (Width) | Minimum Rafter | Recommended |
|---|---|---|
| Up to 8 ft | 2x6 | 2x8 |
| 8-12 ft | 2x8 | 2x10 |
| 12-16 ft | 2x10 | 2x12 |
For beams, match or exceed the rafter size. Longer pergolas (over 8 feet) should have intermediate posts to keep beam spans reasonable.
Post Setting
For freestanding pergolas, posts need to be anchored properly:
- In-ground: Set posts in concrete footings. Bury at least 1/3 of the total post length, minimum 24 inches deep.
- Post bases: Surface-mount hardware bolted to a concrete slab or footing. No burial needed, but the footing must be adequate.
Material Choices
Pressure-treated pine is the budget option. Cedar resists rot naturally and weathers to a silver-gray. Redwood is premium but expensive. For a painted look, consider Douglas fir. Budget roughly $3-8 per board foot depending on species and grade.