6x6 Lumber

6x6 lumber is the square wood post you buy for deck supports, pergolas, porches and heavy framing. Choose free-of-heart-center timber for visible work because excluding the tree’s center reduces twisting, warping and checking as it dries. For posts facing wet ground, get the treatment right first: spring snowmelt in Montana can keep the ground line wet for weeks.

6x6 Pole Barn Posts

A 6x6 pole barn post belongs in the support system for a post-frame shop or barn. Start with the exposure at its base. A buried post needs an explicit ground-contact designation; that is the buying distinction that matters when the ground stays wet after the snow disappears.

A PT 6x6 post means a pressure-treated post. Pressure treatment forces preservatives into the wood to resist decay and insects. For a 6x6 fence post or buried building post, choose treatment designated for ground contact. For a post supported above the soil, choose for its weather exposure and the building’s structural design.

Keep treatment and strength separate in your buying decision. Species and structural grade affect strength; treatment addresses decay exposure. A pole-barn roof also puts snow weight into those posts, so select the lumber, bearing and connections as one support system.

.60-Treated 6x6 Timbers: Choose Your Length

WBC’s .60-treated 6x6 timbers come in 8-, 10-, 12-, 14-, 16- and 20-foot lengths. These are the treated timbers to choose for exterior support work, with ground-contact suitability established separately for any buried application. Keep the .60 treatment designation and the ground-contact designation as separate buying details.

Timber size	Length	Treatment designation
6x6	8 feet	.60
6x6	10 feet	.60
6x6	12 feet	.60
6x6	14 feet	.60
6x6	16 feet	.60
6x6	20 feet	.60

For a 6x6 deck post, buy the length that covers the complete post in the support detail, including its connection to the beam. For a buried post, include the designed embedment in that length. The 20-foot .60-treated 6x6 answers the search for a long treated timber; its length is a cutting and layout choice, not an allowable unsupported post height.

Green lumber shrinks as it dries, and green-treated wood can crack during drying. Allow for that movement when planning visible trim and connections. Treatment protects against decay; drying condition is a separate choice that affects how the finished work looks.

#1 FOHC Kiln-Dried Douglas Fir: Buy It for Visible Posts

WBC’s #1 free-of-heart-center, kiln-dried Douglas Fir 6x6 is the pick for visible porch and pergola posts where the exposure suits the wood. FOHC means the timber was cut to exclude the tree’s heart center, or pith. That reduces the tendency to twist, warp and develop drying checks. Buy that selection where a crooked face or opened check will stare back at you every time you walk onto the porch.

The three designations tell you different things. #1 identifies the grade. FOHC identifies how the timber was cut relative to the heart center. Kiln-dried identifies its drying condition. A #1 grade by itself does not mean dry, and FOHC timber can also be sold green. Choose the full combination for appearance-conscious work.

That matters on the exposed timber porches common around Flathead log homes. The post is part of the finished architecture. For a 6x6 pergola post, make appearance and weather exposure part of the same decision: FOHC addresses drying movement, while treatment addresses decay exposure.

6x6 Post Caps and Post-to-Beam Connections

For a structural 6x6 post cap or 6x6 post-to-beam connector, choose a post cap or beam saddle that matches the beam, post and connection design. These connectors fasten the beam to the post. Adequate bearing matters just as much: too little contact area can crush wood fibers where the beam rests.

A nominal 6x6 post can measure 5-1/2 by 5-1/2 inches. Match the connector opening to the timber’s actual dimensions. Buy the post and connection hardware as a matched assembly, not as two unrelated purchases.

A solar 6x6 post cap belongs in your lighting and finish choices. A structural cap or saddle belongs in the beam connection. Keep those jobs separate when ordering.

Can you notch a 6x6 deck post for a beam? Use a notch that is part of the structural connection design, with the remaining post section and beam bearing accounted for. Establish footing size, post height, bracing and connections through the project’s structural design and applicable local requirements before cutting.

Footings, Cutting and Wrapping a 6x6 Post

Choose the footing for the supported load and the soil, then size the Sonotube and auger around that footing detail. The post’s 6x6 cross section does not determine the hole diameter. Around Polson, clay, gravel and boulders can change across one lot; that ground deserves as much attention as the timber above it.

For cutting a 6x6 deck post, lay out a square cut around the timber and use a wood-cutting saw setup suited to the full section. Predrill for large bolts or structural fasteners to reduce splitting.

For a wood-wrapped post, plan the wrap around the post’s drying movement and keep water from collecting inside the enclosure. Choose the structural post for its load and exposure first, then build the finished appearance around it.

The Pick

Buy WBC’s .60-treated 6x6 timber for exterior deck and outdoor support work, choosing from 8 through 20 feet to cover the complete post detail. For buried fence or pole-barn work, choose an explicitly ground-contact-rated 6x6.

Buy WBC’s #1 FOHC kiln-dried Douglas Fir 6x6 for visible porch, pergola and timber-frame posts where appearance matters and the exposure suits the wood. Pair either choice with the structural post cap or beam saddle the connection needs.

Frequently Asked Questions

Can you put a pressure-treated 6x6 post in the ground?

Yes, if the timber is explicitly rated for ground contact. Pressure treatment puts preservatives into the wood to resist decay and insects, but you shouldn’t treat the .60 designation alone as permission to bury it. For a buried post, make the ground-contact rating part of your selection from the start.

What size is a 6x6 wood post actually?

A common actual size for a 6x6 wood post is 5-1/2 by 5-1/2 inches. Rough full-dimension material can measure differently, so measure the timber before laying out a wrap or fitting a post cap. That difference matters when hardware needs to fit closely around the wood.

What kind of 6x6 should you use for pergola posts?

For visible 6x6 pergola posts, #1 FOHC kiln-dried Douglas Fir is a good pick where the exposure suits the wood. FOHC excludes the tree’s center, reducing the tendency to twist, warp and check during drying, but it doesn’t make the timber immune to movement. Keep that appearance choice separate from treatment: a buried post still needs an explicit ground-contact rating.

How do you cut a 6x6 deck post?

For a square cut on a 6x6 deck post, mark the cut around all four faces and secure the timber before sawing. If your saw can’t cut through in one pass, rotate and secure the post again, then follow the layout on the next face. Support the offcut so it doesn’t tear wood away as the cut finishes.

What kind of post cap connects a 6x6 post to a beam?

A structural post cap or beam saddle fastens the beam to a 6x6 post; a decorative solar cap serves a different job. Fit matters, but the beam also needs adequate bearing where it rests on the post. Keep the bearing surface intact when fitting the connection, because too little contact area can crush the wood fibers.