Pergola Materials Calculator
A freestanding wood pergola is posts in concrete, a beam along each side, rafters across the beams and, if you want more shade, slats across the rafters. Enter the footprint, how many posts carry each beam, the post height, overhang and spacing. The calculator gives a cut list with the stock lengths to buy and the bags of concrete for the post holes, so you can price it at the lumber yard.
Shopping for someone? See our backyard gift guide for deck builders & DIYers.
Compare kits and aluminium systems with the pergola cost calculator.
Cutting rafters or slats to length? The lumber calculator.
Setting pergola posts on piers? The Sonotube calculator.
Pergola materials by size
Four 6x6 posts in 12 in × 36 in holes, doubled beams, 1 ft overhangs, rafters 16 in apart, 80 lb bags.
| Pergola | Beam boards | Rafters | Concrete |
|---|---|---|---|
| 8 × 8 ft | 4 × 10 ft | 7 × 10 ft | 12 bags |
| 10 × 10 ft | 4 × 12 ft | 9 × 12 ft | 12 bags |
| 12 × 10 ft | 4 × 14 ft | 10 × 12 ft | 12 bags |
| 12 × 12 ft | 4 × 14 ft | 10 × 14 ft | 12 bags |
| 16 × 12 ft | 4 × 18 ft | 13 × 14 ft | 12 bags |
How a wood pergola goes together
Set the posts in concrete below the frost line, cut them level, then fix a beam along each side — usually two boards either side of the post tops, bolted through. Rafters sit across the beams at even spacing and overhang both ends; slats across the rafters add shade. The concrete count uses QUIKRETE Concrete Mix's published yields: about 0.60 cu ft from an 80 lb bag and 0.45 cu ft from a 60 lb bag.
This calculator lists materials; it doesn't size the beams. Building on a deck instead of the ground? The deck framing below has to carry the posts — check it with the deck post calculator and the deck footing calculator. To price the whole build, including kits and aluminium systems, use the pergola cost calculator.
Get the Smart Decking Calculator app for Android
Estimate decks on the go, save projects, and share them with contractors.
Building something else? Try our sister calculators
Smart Fencing Calculator
Estimate fence cost by material and linear footage.
Smart Roofing Calculator
Free roof replacement cost estimates by material.
Smart Drywall Calculator
Android app — drywall sheets, mud, and tape estimates.
Smart Fencing Calculator
Android app — fence cost estimates on the go.
Frequently asked questions
- What materials do I need to build a pergola?
- Posts, two beams (often doubled boards), rafters across the beams, optional slats across the rafters, concrete for the post holes and structural screws or bolts. A 12 × 10 ft pergola with four 6x6 posts, doubled beams and rafters 16 in apart needs 4 posts, 4 beam boards, 10 rafters and about 12 bags of 80 lb concrete.
- How many bags of concrete for a pergola post?
- A 12 in hole 36 in deep holds π × 0.5² × 3 = 2.36 cu ft; a 6x6 post takes up 0.63 cu ft of that, leaving 1.73 cu ft. QUIKRETE's 80 lb bag yields about 0.60 cu ft, so roughly 3 bags a post, or 12 for four posts.
- How far apart should pergola rafters be?
- Pergola rafters are commonly set 12 to 24 in apart; closer spacing gives more shade. The calculator counts them for 12, 16 or 24 in — the count is the length divided by the spacing, rounded up, plus one.
- How deep should pergola posts be?
- Deep enough to reach below your local frost line and to hold the posts against wind. Your building department sets the frost depth; enter it as the hole depth and the calculator sizes the posts and concrete to match.
- Should a pergola use 4x4 or 6x6 posts?
- 6x6 posts are stiffer and give more bearing for doubled beams, which is why they're the usual choice for freestanding pergolas; 4x4s suit small or attached structures. Your plan or building department decides for your size and loads.
