What is the Weight of Pressure Treated Lumber 6x6x8′?

If you’ve ever worked on an outdoor project like building a deck, pergola, or fence posts, you’ve probably used pressure-treated lumber. One common size is the 6x6x8 foot post, often chosen for its strength and durability. But before you plan your project, it’s important to know: What does a 6x6x8′ pressure treated lumber weigh? Understanding the weight helps in calculating load capacity, transporting wood safely, and ensuring proper structural design.

Understanding Pressure-Treated Lumber

Pressure-treated lumber is wood that has been infused with preservatives to protect it from rot, insects, and harsh weather. This process adds extra moisture and chemicals to the wood, which makes it heavier than untreated lumber.

Here’s how the weight is influenced:

• Type of wood — Different wood species have different densities. Southern Yellow Pine is commonly used for pressure-treated posts and is fairly heavy.
• Moisture content — Freshly treated lumber can hold a lot of water, increasing weight. Over time, as it dries, the weight will slightly reduce.
• Preservative chemicals — Chemicals like alkaline copper quaternary (ACQ) or micronized copper azole (MCA) add extra mass.

Nominal Size vs Actual Size

Before we calculate the weight, it’s important to understand that lumber sizes are nominal measurements. A “6×6” post doesn’t actually measure 6 inches by 6 inches when manufactured.

• Nominal size: 6 inches x 6 inches x 8 feet
• Actual size: Approximately 5.5 inches x 5.5 inches x 8 feet

This difference slightly affects the total volume and therefore the weight calculation.

Average Weight of 6x6x8’ Pressure Treated Lumber

The weight can vary depending on whether the lumber is freshly treated (wet) or has been drying for months.

Freshly Treated (Wet)

• Density (Southern Yellow Pine with treatment): ~ 60–70 lbs per cubic foot
• Calculated volume: 5.5″ x 5.5″ x 96″ = 2,904 cubic inches = 1.68 cubic feet
• Weight: 1.68 cu ft × ~ 65 lbs/cu ft ≈ 110 pounds

Dried (After Seasoning)

• Dry density: ~ 50 lbs per cubic foot
• Weight: 1.68 cu ft × 50 lbs/cu ft ≈ 84 pounds

So, the average weight range for a 6x6x8′ pressure treated post is between 84 and 110 pounds, depending on moisture content.

Practical Example

Let’s say you’re building a pergola with four 6x6x8′ posts. If the lumber is fresh from the store and still wet, the total weight could be about:

4 posts × 110 lbs = 440 lbs

If you’re transporting these in a pickup truck, you’d need to ensure the vehicle can safely handle the load. You may also need help lifting them, because each post weighs roughly the same as a large adult.

Factors That Affect Weight

1. Wood Species

Southern Yellow Pine is heavier than Spruce or Fir, so the choice of base wood impacts the final weight.

2. Treatment Retention

The amount of preservative retained depends on intended use (above ground vs ground contact). Ground contact lumber retains more chemicals and weighs slightly more.

3. Age of Lumber

If your project uses lumber stored for months in a dry environment, expect lower weights compared to freshly treated wood straight from the mill.

Summary Table of 6x6x8′ Pressure Treated Lumber Weights

Key Points to Remember

• Nominal size is larger than actual size — always use actual dimensions for weight calculations.
• Freshly treated lumber is significantly heavier due to moisture and treatment chemicals.
• Weight can drop by 20–30% as the wood dries over time.
• Always consider weight when planning transportation and handling — it’s easy to underestimate.

💡 Final Thought

Knowing the weight of a 6x6x8′ pressure treated post is more than just trivia — it’s crucial for safe handling, load planning, and project efficiency. Whether you’re a DIY enthusiast building a sturdy fence or a contractor managing a large decking project, factoring in weight ensures better preparation and safety. Next time you lift one of these posts, you’ll have a clear idea of just how much strength you’re using!