Pressure-Treated Fence Calculator
Plan pine privacy fences with accurate counts for pressure-treated pickets, ground-contact posts, rails, and concrete bags.
Fence calculator
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Overview
Pressure-treated pine (PT pine) is the most popular, cost-effective fencing material in North America. Chemical preservatives forced deep into wood fibers protect against termite infestation, fungal decay, and fungal rot.
Because pressure-treated lumber arrives moist from the chemical treatment plant, pickets must be installed tightly butted together since they shrink as they dry in outdoor sun.
Common mistakes
- Leaving wide gaps between wet pressure-treated pickets during installation, resulting in huge unsightly cracks after the wood shrinks.
- Purchasing Above Ground (UC3B) rated posts instead of Ground Contact (UC4A) rated posts for below-grade installation.
- Applying exterior paint or water-sealant before wet pressure-treated lumber has fully dried out over several months.
- Using interior screws that corrode quickly from copper chemical reactions inside pressure-treated lumber.
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Related reading
In-depth guides
Frequently asked questions
How long should you wait before staining pressure-treated pine?
Wait 2 to 6 months until the wood passes the splash test: sprinkle water drops on the board, and if they soak in rather than beading up, the wood is ready for oil-based stain.
Why do pressure-treated pickets shrink after installation?
PT lumber is saturated with water and preservative solutions during manufacturing. As boards dry in outdoor air, pickets shrink across their width by up to 1/8 to 1/4 inch.
What is the difference between UC3B and UC4A ratings?
UC3B is rated for Above Ground use only (like rails and pickets). UC4A is rated for Ground Contact and must be used on posts embedded in earth or concrete.
How many posts are needed for 150 feet of pressure-treated fence?
At standard 8-foot post spacing, 150 feet requires 19 sections, meaning 20 line and end posts, plus additional posts for gate openings.
Do pressure-treated fence posts require gravel beneath them?
Yes. Placing 4 to 6 inches of crushed gravel at the bottom of each post hole lets surface water drain away and stops the bottom end grain from soaking in stagnant water.
Can pressure-treated lumber cause fastener corrosion?
Yes. Micronized copper preservatives are corrosive to plain steel. Always use hot-dipped galvanized (ASTM A153) or polymer-coated exterior wood screws.
How long does a pressure-treated pine fence last?
A pressure-treated pine fence regularly maintained and sealed every 2 to 3 years typically lasts 15 to 20 years before requiring structural rail or post replacement.
What size rails should be used on a 6-foot PT fence?
Use three 2x4 horizontal backer rails per 8-foot bay. Two rails are insufficient and allow 6-foot pickets to bow and cup in direct sun.