Count by exposed width, not board width
On a board-on-board fence each board overlaps its neighbour, so the width that actually covers the run is the board width minus the overlap. Divide the run by that exposed width to get the board count for one side.
A 100 ft (1200 in) run with 6 in boards and a 1 in overlap: each board exposes 5 in, so 1200 ÷ 5 = 240 boards. Round up, then add a few for cuts and waste.
Why it takes more wood than a plain privacy fence
A single-layer privacy fence butts boards edge to edge, so a 6 in board covers a full 6 in. Overlapping to 5 in of coverage pushes the count up by a fifth for the same run — and that is before any gap between overlapped boards is added.
Same 100 ft run, same 6 in boards. The 1 in overlap on each board adds 40 boards — 20% more wood for a gap-free look from both sides.
Board count for a 100 ft run
| Board width | Overlap | Exposed | Boards (one side) |
|---|---|---|---|
| 6 in | 0.5 in | 5.5 in | 219 |
| 6 in | 1 in | 5 in | 240 |
| 6 in | 1.5 in | 4.5 in | 267 |
| 5.5 in | 1 in | 4.5 in | 267 |
| 8 in | 1 in | 7 in | 172 |
Boards run vertically, so height does not change the count — a 4 ft and an 8 ft fence over the same run need the same number of boards, just longer ones.
Before you order
- Posts. One post every 6 to 8 ft, plus one to close the last section. A 100 ft run at 8 ft spacing is 13 posts.
- Allow for shrinkage. Pressure-treated boards are often wet when sold and shrink as they dry. A little overlap protects against gaps opening later.
- Add waste. Order about 5% extra for miscuts, warped boards and offcuts at posts.
Common questions
How many boards does a board-on-board fence need?
Divide the run by the exposed width of each board, which is the board width minus the overlap. A 100 ft run with 6-inch boards overlapping 1 inch exposes 5 inches each, so 1200 in / 5 in is 240 boards. A plain privacy fence over the same run needs only about 200.
What overlap should I use?
One inch is typical. More overlap gives a fuller look and better wind and privacy coverage but uses more boards; less overlap risks gaps opening as the wood dries and shrinks. Half an inch to one and a half inches is the normal range.
Why does board-on-board use so much more wood?
Each board only shows part of its width because the next board laps over the edge. You are paying for width you cannot see. Expect roughly 20 to 40 percent more boards than a gap-free single-layer fence.
