Pergola Lumber Guide for 4x4 and 6x6 Bracket Kits: Sizes, Species and Board Counts

For a pergola built with steel bracket kits, the posts and the top frame beams are all the same size: nominal 4x4 or nominal 6x6 lumber, matched to the kit you buy. Anything you add on top, such as rafters or slats, is your choice and is usually 2x lumber laid across the frame. The kit sets the post size; your layout sets the board lengths.

That makes the lumber question simpler than it is for a cut-and-notch pergola, but two details catch people out. The boards must be dressed to the right actual size to slide into the brackets, and the species and treatment you pick decide how the wood ages outdoors.

This guide covers sizes, the 4x4 versus 6x6 decision, beams and rafters, species, treated lumber, and the board count for each kit layout.

What Size Lumber Does a Bracket-Kit Pergola Need?

Part	Typical size	Who decides	Notes
Posts	4x4 or 6x6	The kit	Must match the kit's post size exactly
Frame beams	Same as the posts	The kit	Slide into the corner and center brackets
Rafters (optional)	Often 2x4 to 2x8	You	Sit on top of the frame; attached with your own fasteners
Top slats or purlins (optional)	Often 2x2 or 2x3	You	Run across the rafters for extra shade
Board lengths	Posts 8 ft recommended, 10 ft maximum; beams set by your bay size	You, within the kit's guidance	Wood span between adjacent brackets: 12 ft recommended, 14 ft maximum

Nominal vs Actual Lumber Sizes

A "4x4" is a label, not a measurement. The American Softwood Lumber Standard (PS 20) defines nominal size as a designation that is larger than the dressed size, and it sets the minimum dressed sizes that graded lumber must meet.

Nominal size	Actual dressed size (dry)	Role in a bracket pergola
2x4	1.5 x 3.5 in	Light rafters or top slats
2x6	1.5 x 5.5 in	Common rafter size
2x8	1.5 x 7.25 in	Deeper rafters for a bolder look
2x10	1.5 x 9.25 in	Rarely needed on top of a kit frame
4x4	3.5 x 3.5 in	Posts and beams for 4x4 kits
6x6	5.5 x 5.5 in	Posts and beams for 6x6 kits

Jurrque brackets are made for dressed (planed) lumber. The 4x4 bracket opening is 3.61 x 3.61 in and the 6x6 opening is 5.62 x 5.62 in, so the two kit sizes are not interchangeable. That leaves only about a tenth of an inch of total play with a standard board, which is why the build instructions say the wood must be dry and straight.

Why Rough-Sawn and Wet Lumber Cause Problems

Rough-sawn lumber has not been planed to standard size, so it is usually too big for the brackets. Moisture matters too. PS 20 allows wood surfaced green to be slightly larger than dry wood; a green 4x4 can be 3-9/16 in, and green cedar or redwood 6x6 stock can be 5-9/16 in wide. Those boards still fit on paper, with only a few hundredths of an inch to spare.

PS 20 also notes that lumber 5 in and thicker, which includes 6x6 posts, is often sold without drying. Wet wood shrinks as it dries, so a board that fits snugly in the store can loosen, twist or check after assembly. Look for a dry stamp (S-DRY or KD) on 4x4s, ask how long 6x6 stock has been drying, and test the fit with a bracket.

4x4 or 6x6 Pergola Posts: How to Choose

Many backyard pergolas are built on 4x4 posts, and many use 6x6. With a bracket kit you choose once, because every post and frame beam follows that size. A 6x6 has about 2.5 times the cross-sectional area of a 4x4 (30.25 vs 12.25 sq in), which shows in both looks and handling.

Factor	4x4 posts	6x6 posts
Look	Light, open frame that suits small patios	Chunkier frame that holds its own on a large patio or next to a big house wall
Weight to handle	An 8 ft board is manageable for one person	Much heavier, especially treated and wet; plan on two people
Straight stock	Widely stocked; easy to sort for straight boards	Fewer boards to choose from; often sold green
Lumber cost	Lower per board	Noticeably higher per board
Kit options	4-post, 6-post, extension, wall-mount, sloped and A-type kits	4-post, 6-post and extension kits

Shop by size in the 4x4 pergola bracket kits or the 6x6 pergola bracket kits. Wall-mount, sloped-roof and A-type kits come in 4x4 only.

Both post sizes use the same span and post-length guidance, covered below. What changes the answer is what you add and where you build: for a roof or shade cover, an exposed site, or local wind and snow conditions, your local building department can tell you what applies, and a qualified professional can size members for a heavy roof.

Beams, Rafters and Top Slats on a Bracket Frame

Frame Beams Go in the Brackets

In a bracket-kit pergola, the top frame is made of the same lumber as the posts. Each corner bracket takes two beams and a post; each center bracket on a double-bay kit takes three beams and a post. A 4x4 kit therefore uses 4x4 beams, and a 6x6 kit uses 6x6 beams. Deeper boards such as 2x8s will not fit the bracket sockets.

Jurrque's recommended wood span is 12 ft between two adjacent brackets, which is one bay, and the maximum is 14 ft. Posts are recommended at 8 ft, with a maximum of 10 ft. A standard frame is a 12 ft span on 8 ft posts, and the largest is a 14 ft span on 10 ft posts. If you plan a roof, shade panels or another added load, confirm the design with your local building department.

Rafters Sit on Top

Rafters are optional. They run across the frame and rest on the top faces of the beams, so they are not limited by the bracket size. Common choices are 2x4, 2x6 or 2x8, depending on the look you want and how far they span. Jurrque kits do not include rafter hardware, so attach rafters conventionally, for example with rafter ties or structural screws chosen from the fastener maker's instructions.

Plan a small overhang past each side beam. Rafter length is the frame width plus both overhangs, so a 10 ft frame with 12 in overhangs needs 12 ft boards.

Rafter Spacing and Shade

On an open pergola, rafter spacing is mostly about shade and looks. Closer spacing and deeper boards cast more shade; wider spacing feels more open. LSU AgCenter's pergola guide describes 12 to 16 in on center as a common spacing for rafters, with optional 2x2 top runners across them for extra shade. Which way the rafters run relative to the sun's path also changes which hours of the day are shaded.

Post Spacing and Where Span Numbers Come From

With a bracket kit, post spacing is simply your beam length, because the brackets connect beam ends to posts. A bay of 13 or 14 ft still works with a single kit. Only when one run between brackets would be longer than 14 ft do you need more bays, from a 6-post kit, an extension kit or a second kit.

For rafter spans, the American Wood Council span calculator gives allowable spans by species, grade, size and spacing for the design conditions you enter. Building departments use code span tables in the same way. A pergola with a solid roof, a long span or an exposed site is worth checking with your building department before you buy lumber.

Best Wood for a Pergola: Species Compared

Any species that comes dressed to the right size, dry and straight will fit the brackets. The difference is how it handles weather, how it looks and what it costs. The USDA Forest Products Laboratory's Wood Handbook groups species by the natural decay resistance of their heartwood. Sapwood, the paler outer wood, has little natural resistance in any species.

Option	Decay resistance	4x4 and 6x6 availability	Weight and handling	Cost tier	Notes
Pressure-treated southern yellow pine	Comes from the preservative; most untreated pine is grouped as slightly or nonresistant	Widely stocked in both sizes at home centers	Heavy, more so when freshly treated	Lowest	Often sold wet; let it dry before staining
Western red cedar	Heartwood grouped as resistant	4x4 common; 6x6 less common and often rough-sawn	Light and easy to cut	Mid to high	Soft, so it dents easily; check every board's size
Douglas fir	Heartwood moderately resistant	Most common in Western markets; often sold as timbers	Moderate to heavy; stiff	Low to mid	Usually needs treatment or a good finish outdoors
Redwood	Old-growth heartwood resistant; young-growth moderately resistant	Regional, mostly the West	Light to moderate	High	Rich color; choose heartwood grades
Composite or PVC post wraps	Covers only; the post inside does the work	Sold as sleeves	Adds thickness	Varies	A wrapped post will not fit inside a bracket socket

The Wood Handbook also notes that natural decay resistance may be lower in ground contact and in warm, humid climates, such as the Gulf Coast and Florida. There, treated lumber or well-maintained heartwood is the safer choice for posts.

Cedar vs Pressure-Treated for a Pergola

Choose pressure-treated pine if budget, availability of straight 6x6s and decay protection are your priorities, and you are happy to stain or paint once it dries. Choose cedar if you want a natural finish, lighter boards and a frame that looks good with only a clear sealer, and you can find dressed 4x4s or 6x6s that fit. Some builders use treated posts and cedar beams; that works with brackets as long as every board measures the same. To see how species and post size change the lumber bill for each kit, see our breakdown of whether it is cheaper to buy or build a pergola.

Pressure-Treated Lumber and Galvanized Hardware

Treated lumber is labeled by use category on its end tag or stamp. The American Wood Protection Association (AWPA) lists structural posts under ground contact, Use Category 4A (UC4A) or higher. UC4B covers heavy-duty ground contact, such as permanent wood foundations. AWPA also notes that above-ground parts that are hard to replace or critical to the structure may call for ground-contact treatment. For pergola posts, buying UC4A stock is a sensible default even when they sit in post bases.

Preservative-treated wood is more corrosive to metal than untreated wood. The International Residential Code section on fasteners in treated wood (IRC R317.3) calls for hot-dipped galvanized steel, stainless steel, silicon bronze or copper fasteners, with connector coatings following the connector maker's recommendations. Jurrque brackets are galvanized steel with a black powder-coated finish. For anything you add, such as rafter ties, extra screws or anchors, choose products the manufacturer lists for use with treated lumber.

Keep treated boards dry and flat until assembly. Freshly treated lumber is often wet, and some yards stock kiln-dried-after-treatment (KDAT) boards, which shrink less after assembly and take stain sooner. Wear gloves and a dust mask when cutting treated wood, and do not burn the offcuts.

How Many Boards Does Each Kit Need?

Every frame member is the same nominal size as the posts, and the kit layout fixes the count. A 4-post kit takes 4 posts and 4 beams, a 6-post kit takes 6 posts and 7 beams, and a 6-post kit plus the extension kit takes 8 posts and 10 beams. The 4x4-only wall-mount kits take 2 posts and 3 beams (single bay) or 3 posts and 5 beams (double). Beam length equals your bay size, so a 10 ft x 10 ft single bay is four 8 ft posts and four 10 ft beams.

The 4-post pergola bracket kit and the 6-post pergola bracket kit come in both post sizes. On wall-mount kits, the wall-to-front beams slope at 15°, so measure along the beam, not across the ground, when you choose board length. The 4x4-only sloped-roof kits follow the same pattern: the 4-post sloped kit takes 4 posts and 4 beams (2 sloped beams front to back and 2 level beams across), and the double sloped kit takes 6 posts and 7 beams (3 sloped and 4 level). The A-type kit takes 4 posts and 9 top pieces: 4 level frame beams, 4 rafters (2 per gable end) and 1 ridge beam. Measure sloped beams and rafters along their length, and dry-fit one gable before you cut all four rafters, because the brackets set the roof angle.

For your own sizes, the lumber calculator below turns bay length, depth and post height into a board list at common stock lengths.

For plan views of every layout, lumber lists for common sizes such as 10x10, 12x12 and 10x20, and how to count rafters and slats, see the pergola plans and lumber lists by kit.

Supplies to Build a Pergola: Full Checklist

Here is everything a bracket build typically involves, beyond what ships in the box. For a side-by-side look at what a bracket kit includes compared with an all-in-one kit, see bracket kits vs complete pergola kits.

• Included in a Jurrque kit: corner brackets (plus center brackets on double-bay kits), post bases, wood screws and expansion bolts.
• Frame lumber: posts and beams from the board counts above, plus one spare.
• Top layer (optional): rafters, slats or shade fabric, and fasteners listed for treated lumber if you use it.
• Anchors for your surface: the expansion bolts are for concrete or masonry; decks, pavers and soil need a different plan, covered in how to anchor a pergola.
• Finish: stain, paint or clear sealer, an end-grain sealer and brushes.
• Tools: ladders, drill, tape measure and cardboard (from the build instructions), plus a saw, level, square, clamps and, for concrete, a hammer drill with a masonry bit.
• Safety: gloves, eye protection and a dust mask for cutting.

How to Pick Boards at the Lumber Yard

• Bring a bracket. Jurrque's instructions suggest taking one to the store. Slide it over the end of each board you pick.
• Sight down every board. Reject boards with a bow, crook or twist you can see from one end; the brackets hold the ends but cannot pull a warped board straight.
• Check moisture. Read the stamp, feel for cold, damp wood, and weigh it in your hands against its neighbors.
• Inspect the ends. Avoid wane (missing corners), large knots and splits in the last foot of each board, where it sits in a bracket.
• Measure length. Boards often run a little longer than the label (PS 20 allows 2x lumber up to 3 in over its nominal length), so cut every post to the same exact length.
• Buy a spare. One extra post or beam is cheaper than a second trip.
• Plan transport. 10 ft and 12 ft boards need a truck, a roof rack with flags, or delivery.

Should You Finish the Lumber Before Assembly?

The faces of each board that sit inside a bracket are hard to reach once the frame is built, so stain or seal all four sides and both ends before assembly. Give extra attention to end grain, which soaks up water fastest, and especially to the bottom of each post, which sits in a post base.

Let wet treated lumber dry before you stain it. A quick check is to sprinkle water on the surface: if it soaks in, the wood is usually ready; if it beads, wait. Install post bases on a surface that drains, and keep soil, mulch and standing water away from them. The pergola build instructions show the assembly order for each kit, and the full bracket-kit build guide walks through the project from planning to the last screw.

Pergola Lumber FAQs

Are 4x4 Posts Strong Enough for a Pergola?

Many small, open pergolas are built on 4x4 posts, and Jurrque sells kits for both 4x4 and 6x6. Whether 4x4s suit your project depends on post height, bay size, any roof or cover and local conditions, so check with your building department for anything large, roofed or exposed.

How Far Can a 2x8 Span on a Pergola?

It depends on species, grade, spacing and the design conditions where you live. Use the American Wood Council span calculator or your local code tables. On a bracket kit, 2x8s work only as rafters on top, because they will not fit the brackets.

Can I Use 2x4s for Pergola Rafters?

Yes, 2x4s are a common choice for light rafters or top slats on short spans. Deeper boards, such as 2x6s, span farther and cast more shade at the same spacing.

Is Cedar Good for a Pergola?

Yes. Western red cedar heartwood is naturally decay resistant, light to handle and takes a clear finish well. Check that the boards are dressed to 3.5 or 5.5 in, since cedar is often sold rough-sawn.

Should I Use Pressure-Treated Wood for a Pergola?

Pressure-treated pine is the most common budget choice, especially for posts. Choose UC4A ground-contact stock for posts, let it dry before finishing and use hardware suited to treated lumber.

Will 4x6 or 8x8 Posts Work With a Bracket Kit?

No. Jurrque kits are made for square, dressed 4x4 (3.5 x 3.5 in) or 6x6 (5.5 x 5.5 in) lumber, and each kit fits one size only.

Can I Mix Species, Such as Treated Posts and Cedar Beams?

Yes, as long as every board is dressed to the same actual size and fits the brackets. Expect the two woods to look different until they are stained or weathered.