How this calculator works. Posts = (length ÷ section spacing, rounded up) + 1, plus one extra post per gate. Rails = sections × rails per section. Boards = fence length ÷ (board width + gap): 0" gap for privacy, 2.5" for picket, using the true 5.5" face of a nominal 1×6.
Concrete defaults to two 50-lb fast-setting bags per post — the standard for a 4×4 post at 24" depth in an 8–10" hole. Deeper frost-line holes need more; adjust in advanced settings.
Fence math, honestly
Fence materials are simple multiplication; fence quality is all in the posts. A third of each post's height should be underground — 2 feet minimum for a 6-foot privacy fence — and below your local frost line, or winter will heave the fence into a wave. Check your frost depth and your property line before buying anything; both surprises are expensive.
Section spacing is a real choice: 8-foot sections use fewer posts and less concrete, but 6-foot sections are stiffer in wind — the right call for solid privacy fencing in gusty areas, since a privacy fence is effectively a sail.
Rules of thumb per 100 ft (6-ft privacy, 8-ft sections)
| Item | Quantity |
|---|---|
| 4×4 posts (8 ft long) | ≈14 |
| 2×4 rails (8 ft) | ≈39 (3 per section) |
| 1×6 boards (6 ft) | ≈219 |
| Fast-set concrete | ≈28 × 50-lb bags |
Buying tips
Use ground-contact pressure-treated lumber for posts — regular treated lumber rots at the soil line. Buy 10% extra boards; warped and split boards hide in every lumber stack, and culling them at the store is your first quality control. Ring-shank nails or exterior screws, never smooth nails: seasonal wood movement pushes those out within two summers.
Common questions
How deep should fence posts go?
One-third of the post height and below frost line, whichever is deeper. A 6-ft fence wants an 8-ft post with 2 ft buried. In cold climates, frost depth (up to 4 ft) governs — check your local code.
Concrete every post, or gravel?
Concrete for gates, corners, and privacy fencing in wind. Gravel-set posts drain better and are easier to replace, and work fine for low picket fencing in firm soil. Many pros do concrete collars over a gravel base — best of both.
Do gates need special posts?
Yes — the hinge post takes constant load. Use a 6×6 (or doubled 4×4), set it deeper, and always in concrete. Sagging gates trace back to undersized hinge posts almost every time.
How much does the wood move?
Expect gaps in a "gap-free" privacy fence: boards shrink up to 1/4 inch as they dry. Butt them tight at install, or use board-on-board style if true privacy year-round matters.