Posts, beams, rafters and shade-slat spacing for a freestanding or attached pergola.
Estimates are planning aids, not an engineered design. Confirm spans, footings and setbacks against your local code and permit before buying.
| Lumber & Decking | $1,266–$1,713 |
| Connectors & Brackets | $153–$207 |
| Concrete & Footings | $119–$161 |
| Fasteners & Hardware | $117–$159 |
| Finishing & Sealant | $68–$92 |
| Total | $1,724–$2,332 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
| Item | Qty |
|---|---|
| Posts — 6×6 Western red cedar2 per beam line · ~8 ft above grade | 4 × 12 ft |
| Beam plies — 2×12 Western red cedar2 × 2-ply built-up beams · 12.0 ft post spacing | 4 × 16 ft |
| Rafters — 2×6 Western red cedarcut to 12.0 ft · 16" on-center | 10 × 16 ft |
| Shade slats — 2×2 Western red cedar21 slats at 6" spacing across the top | 38 × 8 ft |
| Knee brace stock — 4×4 Western red cedar8 braces (2 per post) · ~24" each | 2 × 8 ft |
| Concrete — 80 lb bags4 piers · 12" dia × 42" deep | 20 × bags |
| Exterior stain / UV sealertwo coats on all faces | 2 × gal |
| Item | Qty |
|---|---|
| Post bases (standoff) | 4 × ea |
| Post-to-beam brackets | 4 × ea |
| Rafter / hurricane tiesties each beam crossing | 20 × ea |
| Structural connector screws≈ 264 screws (brackets, braces, slats) | 3 × 100 ct box |
About this planner
Give the Pergola Builder a footprint, post height and material and it lays out the whole structure: post count and depth, built-up beams, rafters at your chosen spacing, the top shade-slat layer, concrete footings, every bracket and screw — plus tools, a cost range and a realistic build time.
Choose freestanding or attached and the framing adjusts — an attached pergola swaps one beam line for a ledger. Open advanced options to set post size, rafter and slat spacing, overhang, frost depth and waste.
Step by step
A high-level walkthrough of the build. Pair it with your plan above and always confirm spans, footings and setbacks against your local code.
Mark the four post centers with batter boards and string. Measure the diagonals and adjust until they're equal — that's how you know the layout is square before anything goes in the ground.
Auger each pier below your frost line, drop in a standoff post base (or set anchor bolts), and pour the concrete. Let it cure before loading the posts.
Stand each post in its base, brace it with temporary 2×4s, and plumb it on two faces with a post level. Leave the posts long — you'll trim them to height next.
Use a water level or laser to transfer one height mark around every post, then cut them all to the same line. Doing this now beats trimming beams overhead later.
Assemble each doubled beam on the ground, then lift it onto the posts and lock it down with post-to-beam brackets. Have a helper — beams are heavy and awkward overhead.
Space the rafters across the beams at your chosen on-center distance, fasten each with a rafter tie, and keep the decorative tails aligned with a string line.
Lay the top slats across the rafters at your spacing, screwing down through each crossing. A spacer block keeps the gaps consistent and the work fast.
Add knee braces at each post for rigidity, sand any rough edges, and apply two coats of stain or UV sealer to every face — including the tops, where water sits.
Equip the job
Hand-picked categories that match the shopping list above. Links open a current selection so you can compare brands and prices.
Keep planning
Answers
Most freestanding pergolas use 6×6 posts with doubled 2×10 or 2×12 beams; 4×4 posts are only really suitable for small, low structures. The planner picks a beam size from your post spacing and defaults to 6×6 posts. Bigger posts also simply look right under a heavy rafter array — undersized posts make the whole thing feel spindly.
Rafters are typically 16–24 inches on-center; tighter spacing looks more substantial and supports more shade slats. The slats (purlins) on top are what actually create shade — space them 2–4 inches apart for heavy shade or 6+ inches for a lighter, airy feel. The tool counts both for you as you change the spacing.
An open slat roof only blocks the sun when it's at an angle, so midday overhead sun still gets through. Closer slat spacing, taller slats set on edge, or running them east–west all increase shade. For full coverage, plan a fabric canopy, shade sail, or polycarbonate panels on top — the slat layer is the structure for it.
A permanent pergola almost always needs concrete pier footings below the frost line for stability, and many jurisdictions require a permit — especially when it's attached to the house. Check local rules before you dig, and call 811 to locate utilities. Freestanding kits on an existing slab are sometimes exempt; confirm locally.