Pergola Materials List: Posts, Beams, Rafters and Slats
Part of the project planner: Planning a shed, pergola, garage slab or coop.
A freestanding 12 × 10 ft pergola, 8 ft high, needs 4 posts of 6×6, 4 boards of 2×10 for two doubled beams, 8 rafters of 2×6 at 24 inch centers, 27 slats of 2×2 and 18 bags of concrete for the footings. This is the full list with the board lengths to ask for, and a chart for other sizes.
The materials list
| What to buy | How much | How we worked it out |
|---|---|---|
| Posts, 6×6 | 4 posts, 10 ft long | Pergola calculator: 2 on each of two sides, no beam span over 12 ft. The 8 ft height needs a 10 ft post to leave room for the beam |
| Beams, 2×10 | 4 boards of 14 ft | Two boards side by side (doubled) on each of the two post rows, each 14 ft long: the 12 ft width plus a 1 ft overhang at each end |
| Rafters, 2×6 | 8 boards of 14 ft | At 24 in centers across the beams, each 13 ft long: the 10 ft depth plus a 1½ ft overhang front and back |
| Slats, 2×2 | 27 pieces of 8 ft | 14 rows across the rafters at 12 in spacing, 14 ft long, with 10% waste |
| Footing concrete | 18 bags of 80 lb | Sonotube calculator: 4 footings 12 in across and 3 ft deep, plus 10% |
| Post bases | 4 standoff bases | Keep the end of the post off the concrete, away from standing water |
| Carriage bolts, ½ in | 16 bolts | Two through each beam where it meets a post |
| Rafter ties | 16 clips | One on each side of every rafter, against uplift in the wind |
Lumber for other pergola sizes
8 ft high, rafters at 24 in, 2×2 slats at 12 in, beams that span no more than 12 ft:
| Pergola | Posts | Beam boards | Rafters | Slats (8 ft) | Footing bags |
|---|---|---|---|---|---|
| 10 × 10 ft | 4 | 4 | 7 | 24 | 18 |
| 12 × 10 ft | 4 | 4 | 8 | 27 | 18 |
| 12 × 12 ft | 4 | 4 | 8 | 31 | 18 |
| 14 × 12 ft | 6 | 4 | 9 | 36 | 26 |
| 16 × 12 ft | 6 | 4 | 10 | 40 | 26 |
| 20 × 12 ft | 6 | 8 | 12 | 49 | 26 |
The pergola calculator lets you change the height, the rafter and slat spacing and the footing size.
Choices that change the list
| Choice | Effect |
|---|---|
| Slats at 12 in, 6 in, or none | 27, 52 or 0 pieces of 2×2 for the 12 × 10 ft size |
| Rafters at 16 in instead of 24 in | 11 rafters instead of 8 |
| A pergola 20 ft wide | 6 posts and 8 beam boards, because of the longer span |
| A taller pergola | Longer posts, and bigger footings in windy places |
Before you build
- Check the permit rules. Many places need a permit for a pergola above a set size, or one attached to a house, and they may set the footing depth.
- Call 811 before you dig the post holes.
- Choose the wood. Pressure-treated lumber, cedar or redwood last outdoors; use exterior-rated, hot-dipped galvanized or stainless fasteners everywhere.
- Check the sizes. The posts, beams, rafters and connections here are typical, but the right sizes depend on your span, your wind and snow loads and your code, so compare them with a span table or a plan.
- Seal all faces of the lumber, including cut ends, before you assemble it.
How the job goes
- Mark the post positions and check they are square by measuring the diagonals (see our check square calculator).
- Dig the footings below the frost line, pour the concrete, and set the post bases or post anchors in the wet concrete.
- Stand the posts plumb and brace them. Mark the beam height on each one with a level.
- Fix the doubled beams to the posts with bolts.
- Set the rafters on the beams at your spacing and tie them in with clips. Cut the ends with a pattern so they match.
- Add the slats across the rafters, then stain or seal the whole structure.
Mistakes that cost people money
- Posts set out of square, which makes every board after them harder to fit.
- A beam spanning more than the lumber can carry. It sags in the first wet season.
- No post bases. Wood sitting in concrete rots from the bottom up.
- Using plain screws or bright nails outdoors. They rust and stain the wood.
See also the deck materials list and fence post spacing and depth. Estimates only: check your local code, and follow the product labels.
Frequently asked questions
How much lumber do I need for a 12x10 pergola?
4 posts of 6×6 (10 ft), 4 boards of 2×10 for the doubled beams, 8 rafters of 2×6 and 27 slats of 2×2 for a 12 × 10 ft pergola, 8 ft high.
How many posts does a pergola need?
Four for a pergola up to about 12 feet wide. A 20 ft wide pergola takes 6, because no beam should span more than about 12 feet.
How far apart should the rafters be?
Usually 16 to 24 inches on center. At 16 inches a 12 ft wide pergola needs 11 rafters instead of 8.
How many slats do I need for shade?
27 slats of 2×2 at 12 inch spacing gives light shade, 52 at 6 inch spacing gives more, and open rafters need none. Closer slats cut more light.
How much concrete do I need for the footings?
18 bags of 80 lb mix for 4 footings 12 inches across and 3 feet deep. Go deeper where the ground freezes.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.