What a 10-Foot Treated 6x6 Actually Measures and What to Verify

A nominal 6x6x10 pressure-treated timber commonly measures 5.5 by 5.5 inches in actual cross-section and 10 feet in listed length, as this Lowe’s 6x6x10 Southern Yellow Pine listing shows. The size is the predictable part. Species, grade, preservative, and use category change from yard to yard, and they decide whether the piece fits the job. Buy from the grade stamp and the treatment end tag on the exact timber, not from the shelf sign.

Pressure treatment addresses biological deterioration. It does not establish allowable load, post height, footing size, embedment, bracing, or connections. Those come from the approved plans and locally applicable code.

Enter the piece length and the deductions from your plans; usable length updates as you type, and the listings comparison sits below it.

Five Checks Decide Whether The Timber Fits

1. Actual dimensions and usable length. Confirm the finished cross-section and the full piece length, then subtract embedment, trimming, damaged-end removal, and connection details.
2. Species and grade. Read the lumber grade stamp. Species and grade set the structural values available to the designer.
3. Treatment category. Read the treatment tag for preservative, use category or exposure, retention, treater, and inspection agency.
4. Structural requirements. Check post height, loads, footing, embedment, bracing, and connections against the current plans and local code.
5. Compatible hardware. Match anchors, bolts, screws, connectors, and flashing to the preservative chemistry and service environment.

Several retail products follow one pattern: nominal 6 x 6 x 10 feet, #2 Southern Yellow Pine, ground-contact label. That pattern does not make them interchangeable. Preservative system, retention, use category, moisture condition, and inspection marks can all differ.

Retailers list decks, docks, retaining walls, pergolas, pole buildings, fences, and landscaping as suggested uses. Those uses carry very different loads, exposures, drainage conditions, and connections. A suggested-use list is a shopping aid, not structural approval for a particular installation.

Actual Size Is 5.5 By 5.5 Inches, And 10 Feet Is Not Installed Height

“6 x 6” is the nominal cross-section and “10” is the listed length in feet. Both the Lowe’s product above and a specific Menards 6x6x10 SKU list an actual size of 5.5 x 5.5 inches by 10 feet.

Menards identifies its product as #2 Southern Yellow Pine treated with MCA and labeled “Ground Contact Critical Structural, UC4B Heavy Duty.” Those specifications apply to that SKU, not to every nominal 6x6.

Menards also warns that dimensions can vary with moisture content and that damp treated wood can shrink as it dries. That matters when brackets, saddles, trim, or drilling templates have tight tolerances. Measure the selected piece before fabricating anything around it.

A 10-foot ordered length does not deliver 10 feet of installed height. Usable installed length equals piece length minus required embedment, minus trimming, minus damaged-end removal, minus connection allowance.

Every deduction comes from the approved design. There is no universal amount to subtract for burial, post bases, beam connections, end cuts, or final elevation.

At pickup, confirm the full length and sight along the piece for bow and twist. If finished elevation is critical, lay out the actual timber rather than relying on its nominal description.

The Grade Stamp And Treatment Tag Answer Different Questions

The grade mark identifies the grading information used to select structural properties. The treatment mark or end tag identifies the treatment and the exposure it is intended for. A timber needs both to be fully specified.

The Southern Forest Products Association says a treated-wood quality mark can identify the use category or end-use exposure, preservative system, retention, treating company, and inspection agency. Its pressure-treated Southern Pine specification guide recommends specifying treated lumber by species, product, preservative, and intended end use rather than simply calling it “pressure treated.”

Confirm	Where	Why
Species	Grade stamp, tag, invoice	Structural values and treatment specs vary by species
Grade	Grade stamp or certificate	Classification used for structural selection
Preservative	Treatment tag, supplier documents	Sets chemistry and hardware compatibility
Use category	Treatment tag	Service condition the treatment covers
Retention	Treatment tag or certificate	Part of the treatment spec for that exposure
Treating company	Treatment mark	Who treated the material
Inspection agency	Grade and treatment marks	Who oversees grading or treatment

Same Nominal Size, Different Timber

The Menards SKU is #2 Southern Yellow Pine, MCA-treated, and labeled UC4B. A Moscow & Pullman Building Supply listing identifies its nominal 6x6x10 as #2-and-better Hemlock Fir treated with CCA .60.

Both are sold as 6x6x10 pressure-treated lumber. They are not equivalent specifications. Species, grade, preservative, and documented exposure all have to be compared.

Do not interpret an isolated label such as “.15” or “.60” without the treatment tag or supporting documentation. The number alone does not establish its units, use category, approved exposure, or equivalence to another product. If the supplier cannot provide the complete treatment information, the timber is not fully specified for comparison.

Ground Contact Is An Exposure Rating, Not A Structural Design

Ground-contact and above-ground treatments are distinct. Lumber labeled only for above-ground use does not go where the member will contact soil or water, or where the plans require a ground-contact category.

A correct ground-contact label still covers only durability. It says nothing about whether the member can carry the proposed load, or whether its height, footing, embedment, bracing, and connections are adequate.

Label on the exact product	Buying decision
Above-ground only	Do not substitute where ground contact is required
Generic ground contact	Verify the exposure and use category the project requires
Specifically labeled UC4B	Applies to that SKU; still verify the structural design

DCA6 Sets A Nominal 6x6 Minimum Only Within Its Scope

The American Wood Council’s DCA6 guide specifies a nominal 6x6 minimum post size for the single-level attached residential decks within that guide’s scope. The guide is based on the 2015 IRC, limits its application to defined deck conditions, and requires materials and construction to be accepted by the authority having jurisdiction.

Post-height limits, loads, footings, bracing, and connections still have to follow the guide or a separate approved design. Read the AWC deck guide and its stated limitations before applying any of its provisions to a project outside that scope.

Inspect Each Piece And Plan The Unload Around Real Weight

A bundle description is not proof of compliance. Check each piece at pickup:

• Match the invoice, SKU, species, treatment, and ordered length.
• Locate a readable grade stamp and treatment tag.
• Sight along all four faces for bow and twist.
• Check for knots, checks, splits, wane, and handling damage.
• Inspect both ends where cuts, connectors, or bearing surfaces are planned.
• Measure the cross-section where brackets or post bases must fit.
• Set aside pieces whose condition interferes with the intended connection, bearing area, layout, or exposed finish.

No single appearance rule rejects every #2 timber. Menards notes that its #2 timbers may contain knots, wane, checks, splits, warping, or twisting. Grade, connection location, finish expectations, and project requirements decide whether an individual piece is suitable.

Menards lists a 90-pound shipping weight for its UC4B Southern Yellow Pine product. That is a SKU-specific figure, not a universal weight for a 6x6x10. Species, treatment, and moisture condition change what the crew actually has to move.

Plan labor, mechanical assistance, transport, and unloading around the actual shipment. Confirm the vehicle, trailer, racks, tie-downs, and lifting equipment stay within their documented limits. Settle the handling plan before a wet 10-foot timber is hanging halfway out of the rack.

Field-Treat Every Cut And Match Hardware To The Preservative

Field cuts, notches, and drilled holes in treated lumber need treatment. The sequence that works:

1. Identify the timber’s original preservative and intended exposure.
2. Make only the cuts, notches, and holes the design requires.
3. Select a field preservative approved for that treatment and exposure.
4. Apply it according to the product instructions.
5. Assemble with compatible fasteners, connectors, anchors, and flashing.

SFPA guidance calls for field treatment of cuts, notches, and drilled holes in accordance with AWPA M4. The guide identifies copper naphthenate and oxine copper as field-treatment options under that standard. The correct product still depends on the original treatment, application, and exposure, so check the field-preservative label before it goes on.

Hot-dip galvanized and stainless steel are supported examples of corrosion-resistant materials for treated-wood fasteners and connectors. The required coating, alloy, and connector specification still depends on the preservative and the environment.

The AWC deck guide prohibits direct aluminum contact with lumber treated with copper-containing preservatives such as ACQ, Copper Azole, or ACZA. That restriction does not mean aluminum is incompatible with every treated product. Verify the preservative chemistry and follow the treatment supplier’s and hardware manufacturer’s compatibility information.

There is no universal post-anchor, bolt, screw, or connection schedule for a nominal 6x6. Hardware selection depends on the load path, member condition, exposure, base detail, treatment chemistry, and approved design.

No Dated Price Survived Review, So Compare The Exact SKU Locally

There is no price range here, because none of the retail figures reviewed could support one. Some quoted prices were tied to a particular branch. Others lacked the location or capture date needed for an apples-to-apples table. The pages also differed in species, grade, treatment, inventory, pickup terms, delivery, and promotions.

A usable quote carries a date, a supplying branch, a quantity, a fulfillment method, and the complete material specification. For a treated 6x6x10 that means actual cross-section and length, species and grade, preservative system, documented exposure or AWPA use category, and retention where the specification requires it.

Then compare the money side: quantity breaks, rebate conditions, pickup, delivery, and handling charges. A time-limited rebate is not the same as an immediate reduction in the purchase price. Ask whether the yard lets you inspect and reject unsuitable pieces.

A lower quote for a generic ground-contact timber is not automatically equivalent to a product carrying a different species, grade, preservative, retention, or use-category mark. Have the branch confirm the SKU and treatment tag, then inspect the pieces before treating two quotes as comparable.

A purchase order that says only “6x6x10 pressure treated” is incomplete. The nominal size gets the yard started; the marks on the timber and the project requirements decide whether it fits the job.

Deck Posts, UC4B Labels, And Finishes

A 6x6x10 Can Be A Deck Post Only Within A Design’s Limits

Nominal size and a treatment label are not enough to approve it. DCA6 uses nominal 6x6 as the minimum post size only for the single-level attached residential decks within its stated scope. Post height, grade, loads, footing, bracing, connections, treatment, approved plans, and locally applicable requirements still control.

UC4B Is Not The Same As A Generic Ground-Contact Label

“Ground contact” can appear as a broad retail description without the complete treatment specification behind it. The Menards product is explicitly labeled “UC4B Heavy Duty” and “Critical Structural,” and those labels apply to that exact SKU. A generic ground-contact description does not establish that another 6x6 carries the same treatment classification.

Painting Or Staining Depends On The Listed Product And The Coating Maker

Some retailer-listed products state that they can be painted or stained. One Home Depot #2 ground-contact Southern Pine post is described as paintable or stainable. Follow the coating manufacturer’s moisture and surface-preparation requirements, and judge readiness by the timber’s condition rather than the purchase date.