# Pergola Calculator

Calculate pergola materials: posts, beams, rafters, and cross pieces. Enter dimensions and spacing to get exact lumber counts and total board feet.

## What this calculates

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.

## Inputs

- **Pergola Length** (ft) — min 4 — The long dimension (direction beams run)
- **Pergola Width** (ft) — min 4 — The short dimension (direction rafters span)
- **Post Height** (ft) — min 6
- **Post Size** — options: 4x4 (3.5" x 3.5"), 6x6 (5.5" x 5.5")
- **Beam / Rafter Size** — options: 2x6 (1.5" x 5.5"), 2x8 (1.5" x 7.25"), 2x10 (1.5" x 9.25"), 2x12 (1.5" x 11.25")
- **Rafter Spacing** — options: 12" on center, 16" on center, 24" on center
- **Cross Piece Spacing** — options: No cross pieces, 6" on center, 8" on center, 12" on center — Small pieces running perpendicular to rafters for shade
- **Rafter Overhang** (in) — min 0, max 36 — How far rafters extend past the beams on each side

## Outputs

- **Posts Needed**
- **Beams Needed** — Doubled beams (2 per side) for bolted connection
- **Rafters Needed**
- **Cross Pieces Needed**
- **Post Lumber** (board ft)
- **Beam & Rafter Lumber** (board ft)
- **Total Board Feet** (board ft) — All lumber including 10% waste
- **Post Hole Depth** (in) — 1/3 of total post length for in-ground setting

## Details

## 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.

## Frequently Asked Questions

**Q: How far apart should pergola posts be?**

A: Posts should be no more than 8 feet apart for 2x8 beams, or up to 10 feet for 2x10 or 2x12 beams. Closer spacing (6 feet) allows smaller lumber but uses more posts. For most residential pergolas, 6-8 foot post spacing is the sweet spot.

**Q: Do I need a permit for a pergola?**

A: It depends on your jurisdiction. Many areas exempt freestanding structures under a certain size (often 120-200 sq ft) from permits. Attached pergolas (bolted to the house) almost always require a permit. Check with your local building department before starting.

**Q: What rafter spacing gives the most shade?**

A: Closer spacing means more shade. At 12 inches on center with 2x8 rafters, you get about 60% shade coverage. At 16 inches on center, about 45%. Adding cross pieces perpendicular to the rafters significantly increases shade without changing rafter spacing.

**Q: How deep should pergola post holes be?**

A: Post holes should be at least 1/3 the total post length and below the frost line. For an 8-foot post, that means burying about 3-4 feet. In cold climates, the frost line may require even deeper holes (36-48 inches). Holes should be 3 times the post width.

**Q: Should I use 4x4 or 6x6 posts?**

A: Use 6x6 posts for pergolas wider than 8 feet or taller than 8 feet. They look more proportional on larger structures and resist racking better. 4x4 posts work fine for small pergolas (under 8x8 feet) or when attached to a house wall for lateral support.

---

Source: https://vastcalc.com/calculators/construction/pergola
Category: Construction
Last updated: 2026-04-08