Pergola Post Sizes Guide: 6×6 to 12×12 — Which Size Do You Need?
Pergola post sizes at Western Timber Frame range from 6×6 to 12×12 inches, but choosing the right one is about more than making the posts thicker. The right size depends on span, engineering requirements, local snow and wind loads, and the architectural presence you want to create. Each post size is paired with one of our engineered timber series — 6,000, 8,000, 10,000, or 12,000 — so the proportions and structural capacity work together. The best post size isn’t the biggest one; it’s the one engineered to your project — and it arrives as a custom-engineered kit, cut to your exact design.
Key takeaways
- The series number tells you the post: 6,000 Series = 6×6, 8,000 = 8×8, 10,000 = 10×10, 12,000 = 12×12. All four are squared timbers; the height is set to your headroom.
- Post size isn’t set by the footprint. You pick it for the look you want; we engineer the structure to your local code either way.
- Every structure is engineered to your local snow and wind loads before a single timber is cut, so the post size is a result of the math, not a guess.
- Douglas Fir is our standard timber for all four series — strong, stable, and the reason a heavier post reads as solid rather than bulky.
- Post size and footprint are two different questions. This guide covers how thick the timbers are; our pergola sizes guide covers how much ground the structure covers.
Looking for costs? Current pricing by size and series is published on our timber structure pricing page.
What the series numbers mean
The name of each series is the post size. A 6,000 Series structure stands on 6×6 timbers; a 12,000 Series stands on 12×12 timbers. The posts are squared — the same measurement front to back as side to side — so a 10×10 is a true ten inches each way. Height isn’t fixed to the series: our standard gives about 8 feet of headroom underneath, and taller is an option when you want more airflow or a more dramatic feel.
These are also full-dimension timbers, not the shrunken lumber sold at a home-improvement store. A Western Timber Frame 6×6 is an actual 6 inches; a home-center 6×6 is milled down to about 5.5 inches. That extra mass — in Douglas Fir, Coast Redwood, or Cedar — is part of why our kits weigh what they do. What changes as you move up the series is the mass of the timber and how much it can carry. A 12×12 post has four times the cross-section of a 6×6, so it spans farther, shoulders more snow, and stands up to stronger wind — and it reads as a much heavier, more substantial frame.
Timber post sizes at a glance
|
Series |
Post size |
Kit weight (14×22) |
Best for |
|---|---|---|---|
|
6,000 Series |
6×6 |
2,925 lbs |
Smaller pergolas and arbors, shorter spans, milder loads — a clean, lighter frame. |
|
8,000 Series |
8×8 |
4,561 lbs |
The popular middle ground — most patio pergolas and pavilions, with a solid, balanced look. |
|
10,000 Series |
10×10 |
6,556 lbs |
Larger structures, longer spans, heavier snow or wind — a strong, stately frame. |
|
12,000 Series |
12×12 |
9,035 lbs |
The largest pavilions and commercial builds, the widest spans, and the most commanding presence. |
Those weights are for the same 14×22 kit in each series, and they tell the real story: going from 6×6 to 12×12 posts more than triples the timber — from about 2,925 lbs to 9,035 lbs. A bigger post never stands alone; it brings heavier beams, rafters, and knee braces with it. That added timber is exactly what lets the larger series span farther and carry more snow.
It’s not just the posts — the whole frame steps up
Move up a series and every member grows with the posts. Here’s the full picture — the beams, rafters, knee braces, and shade planks all get beefier as you go:
|
Series |
Posts |
Beams |
Rafters |
Knee braces |
Shade planks |
|---|---|---|---|---|---|
|
6,000 Series |
6×6 |
3×10 |
2×8 |
2×8 |
2×4 |
|
8,000 Series |
8×8 |
4×12 |
3×10 |
3×8 |
2×6 |
|
10,000 Series |
10×10 |
6×12 |
4×10 |
4×8 |
3×6 |
|
12,000 Series |
12×12 |
8×12 |
6×10 |
6×8 |
4×6 |
These four are our standard series — a starting point, not a ceiling.
Building bigger than 12×12: we’ve gone well past 12×12 — plenty of 14×14 structures, and some as large as 16×16 and even 18×18. Timbers that big carry a bit of character with them. Past about 12×12 they can no longer be milled “free of heart,” so the center of the tree sits inside the timber — what’s called “boxed heart” — and it checks, meaning it develops surface cracks, a little more as it seasons. That’s a natural trait of massive timber, not a weakness, and it doesn’t affect the structure’s strength. On the very largest builds we plan for it, sometimes running through-bolts up a post that can be tightened over time to keep the frame drawn tight as the wood settles.
How to choose your post size
Here’s the part that takes the pressure off: you don’t have to work out which post is strong enough. That’s our job. Every structure is fully engineered to your local building code — wherever you are in the country, and whatever your area has to stand up to — so any size you choose is built to last.
That leaves you free to choose post size for the reason that actually matters to you: the look. A 6×6 frame reads light and clean; a 12×12 reads bold and substantial; the sizes in between land along that range. Pick the one that suits the style and presence you want, and we’ll take care of the spans, the engineering, and everything that keeps it standing.
Post size vs. footprint — two Different questions
It’s easy to blur these together, so it’s worth keeping them apart. Footprint is how much ground your structure covers — a 12×16, an 18×20, and so on. Post size is how thick the timbers are that hold it up. A large footprint doesn’t automatically mean larger posts — on a wider structure we can add posts to keep each span short, so the timbers stay the same. What drives post size is the span between posts and the load, Post size follows the span and the design, not the square footage, and the structure is engineered to hold up wherever it’s built. If you’re still working out how much room you want underneath, start with our pergola sizes guide, then come back to the post size.
How the posts carry the load
The timber size is only part of the strength story — how the timbers join is the rest. Where a post meets a beam, the pieces lock together with our Dovetail Difference®: CNC-precision-cut dovetail joinery that interlocks timber to timber with no visible hardware. The joint itself carries the load, so the frame — what timber framers call the bent, the standing assembly of posts and beams — works as one connected structure rather than a stack of parts bolted together.
At the ground, our EarthAnchor™ foundation system ties the posts down and is engineered to stand up to strong wind. The result is a frame where the post size, the joinery, and the anchoring are all sized to the same engineered load — which is why a Western Timber Frame structure can carry the weight of snow, hang a swing, and hold its line for decades.
When a bigger post is really about the look
Sometimes the load would be fine on a smaller timber, and you choose a larger one anyway — for the substantial, heirloom feel. A 10×10 or 12×12 frame has a presence a lighter post can’t match, the kind of heavy-timber look that stops people in a yard and makes them ask who built it. That’s a legitimate reason to go heavier, and it’s a conversation your design team will have with you rather than a box you check. The post follows both what the structure needs and the feel you’re after.
Whatever size you choose, it ships as a kit
Whatever size you choose, it ships as a custom-engineered kit
Every post size — 6×6 through 12×12 — arrives the same way: as a precision-cut kit, pre-stained and test-fit at our Payson, Utah shop before it ships. The dovetail joints are already machined, the timbers are labeled, and most structures go up in an afternoon to a day. You’re not milling posts or cutting joints in your driveway; the heavy timber shows up ready to stand.
Questions to ask before you pick a post size
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