How to calculate fence materials
Every fence comes down to sections: the spans between posts. Divide each side by the maximum post spacing — 8 ft for wood (Home Depot's install sheet), the panel width for panels, 10 ft for chain link — round up, and space the posts evenly. A straight run needs one more post than it has sections. Each corner shares a post between two sides, and each gate needs two posts of its own.
Worked example — 100 ft of 6-ft wood privacy fence: 100 ÷ 8 = 12.5 → 13 sections at about 7 ft 8 in, so 14 posts. Pickets are 5-1/2 in wide, so 1,200 in ÷ 5.5 = 218.2 → 219 pickets, 241 with 10% extra. Three rails per section is 39 2×4×8s. Each post sits 36 in deep, so you buy 10-ft posts and 56 bags of Fast-Setting concrete (4 per post).
How many pickets per foot?
Use the board's actual width — a “1×6” picket is 5-1/2 in wide, a “1×4” is 3-1/2 in. Divide 12 in by the width plus the gap (or minus the overlap):
| Style | Per foot | Per 8-ft section | Per 100 ft (+10%) |
|---|---|---|---|
| Privacy, 1×6 butted | 2.18 | 18 | 241 |
| Privacy, 1×4 butted | 3.43 | 28 | 378 |
| Board-on-board, 1×6, 1.5 in overlap | 3 | 24 | 330 |
| Board-on-board, 1×6, 1 in overlap | 2.67 | 22 | 294 |
| Spaced picket, 1×4, 2.5 in gap | 2 | 16 | 220 |
| Spaced picket, 1×6, 2.5 in gap | 1.5 | 12 | 165 |
Board-on-board is two staggered layers: each front board covers the gap between two back boards with 1 to 1-1/2 in of overlap per edge, so the fence stays solid after the wood shrinks. That takes about 38% more boards than a butted privacy fence. Home Depot's older sheet lists 19 board-on-board pickets per 8-ft section — the overlap math says 20 to 24, so buy by the math.
How deep should fence posts be?
Quikrete's rule is to bury a third of the post's overall length — the same as half its height above ground — and put gravel under it for drainage. Where the ground freezes, go below your local frost depth; it varies enormously (Minnesota requires 42 in in the south of the state and 60 in in the north for building footings), so ask your building department. Gate posts carry the most load: set them deeper and in bigger holes.
| Fence height | Post in ground | Post length needed | Buy |
|---|---|---|---|
| 4 ft | 24 in | 6' | 8 ft |
| 5 ft | 30 in | 7' 6" | 8 ft |
| 6 ft | 36 in | 9' | 10 ft |
| 8 ft | 48 in | 12' | 12 ft |
That is why 8-ft posts are a common mistake for a 6-ft fence: they leave only 2 ft in the ground. They can work in mild climates and firm soil, but the calculator shows what the rule calls for and lets you choose.
How many bags of concrete per fence post?
Answers online range from half a bag to four or more because they assume different holes. Quikrete's own calculator fills a round hole three times the post width to the very top with no gravel; real installs sit on 4–6 in of gravel and stop 3–4 in below grade so soil can cover the concrete. For a 4×4 in a 10-in hole:
| Hole depth | Quikrete calculator (4 in round post, 12 in hole, filled) | Realistic concrete | 50-lb Fast-Setting | 80-lb Concrete Mix |
|---|---|---|---|---|
| 24 in | 4 bags | 0.65 cu ft | 2 | 2 |
| 30 in | 5 bags | 0.88 cu ft | 3 | 2 |
| 36 in | 6 bags | 1.11 cu ft | 3 | 2 |
| 42 in | 7 bags | 1.34 cu ft | 4 | 3 |
Fast-Setting is poured dry: fill to 3–4 in below grade, then add about a gallon of water per 50-lb bag. Holes deeper than 30 in go in two lifts. Posts take strain after 4 hours, versus 24 hours for regular 80-lb Concrete Mix, which you mix first. Because dry-poured bags can't be shared between holes, count bags post by post — or use the post hole concrete calculator for odd hole sizes.
Rails, fasteners, caps and gates
- Rails: no more than 24 in apart — 2 for fences up to 4 ft, 3 for 5–6 ft, 4 for 7–8 ft. One 2×4×8 per rail per section.
- Fasteners: 2 per picket at every rail (6 per picket on three rails) with 2-in screws or nails, and 3-in fasteners for rails — hot-dip galvanized or stainless, as Home Depot's install sheet specifies.
- Clearance: keep pickets and vinyl bottom rails at least 2 in off the ground.
- Gates: two hinges per leaf and a latch; double drive gates add a drop rod. Leaves wider than about 5 ft sag, and vinyl gate posts need an aluminum stiffener that is sold separately.
- Panels: “6×8” wood panels hold 18 to 28 pickets depending on the product, and posts are never included. Vinyl panels set the post centers: 97 in for 8-ft Catalyst/Veranda Premium panels on 5×5 posts.
Mistakes that cost the most
- Counting posts as length ÷ 8 + 1 for the whole yard — it misses every corner shared between sides and the second post at every gate.
- Forgetting to subtract gate openings from the picket count, or forgetting the gate leaves need pickets too.
- Skipping the call to 811 before digging. It is free, and hitting a buried line is not.
- Building right on the property line. Set posts a few inches inside it and confirm the line with your plat or a survey.
- Staining new pressure-treated wood too soon: Thompson's says wait 30 days; Ready Seal recommends 2–3 months.
Chain link instead? Use the chain link fence calculator. Getting quotes? The fence cost calculator compares installed prices by material. Common jobs: 100 ft privacy fence, 200 ft fence posts, 100 ft vinyl fence.