Board-on-board & shadowbox picket count calculator
Count the boards a board-on-board or shadowbox privacy fence needs, allowing for the overlap between boards and a waste margin.
Calculator
Board-on-board overlaps each 5.50" board by 1.00", so effective coverage is 4.50" — 100 ft takes about 267 boards (buy 294 with waste). Overlap and shadowbox stagger are labeled — measure your pattern.
Board-on-board (also called shadowbox when the boards alternate front and back) is a full-privacy pattern where each vertical board overlaps its neighbor rather than butting against it. The overlap hides the gaps that open as wood shrinks and gives a clean look from both sides — but because every board only covers its width minus the overlap, the fence needs far more boards than a plain butted run. This calculator does that overlap-aware count and adds a waste margin.
It is a material-quantity tool, not a price tool: it tells you how many boards to buy so your order — or a contractor’s takeoff — is right the first time.
Formula
Overlap shrinks the coverage each board contributes:
effective coverage = board width − overlapboards = ceil(length × 12 ÷ effective coverage)boards to buy = ceil(boards × (1 + waste%))
- × 12 converts the run from feet to inches to match the board width.
- ceil rounds up — you cannot buy a fraction of a board.
- waste% covers culled, warped or miscut boards (10% is typical).
Worked example
A 100 ft fence built from 5.5" boards with a 1" overlap and a 10% waste margin:
coverage = 5.5 − 1 = 4.5"boards = ceil(100 × 12 ÷ 4.5) = ceil(266.7) = 267buy = ceil(267 × 1.10) = 294
So plan on 294 boards. The same 100 ft in butted 5.5" boards needs only about 218 — board-on-board uses roughly 35% more lumber, which is exactly why its cost per foot is higher.
Background & practice
Two details decide the count. Overlap is the big lever: a 1.5" overlap instead of 1" drops the effective coverage from 4.5" to 4.0" and adds boards; too little overlap and gaps reappear as the wood dries, too much wastes lumber. Board width matters too — nominal 1×6 boards are 5.5" wide and 1×4 are 3.5", so always enter the real measured width, not the nominal name.
This tool counts the facing boards. A true shadowbox alternates boards on the front and back of the rails, which uses a similar total but splits it two ways — the count here still tells you how many boards to buy. For a plain butted picket or a spaced style, use the picket / board count calculator instead, and to turn the board count into a budget see the wood fence cost tool. Order a little extra beyond the waste figure for corners and end trimming.
Reference table
| Pattern | Effective cover | Boards / 100 ft | +10% waste |
|---|---|---|---|
| 5.5" board, 1" overlap | 4.50" | 267 | 294 |
| 5.5" board, 1.5" overlap | 4.00" | 300 | 330 |
| 3.5" board, 0.75" overlap | 2.75" | 437 | 481 |
| 5.5" boards butted (no overlap) | 5.50" | 219 | 241 |
Board-on-board covers width − overlap per board, so it uses far more boards than a butted run. Widths, overlap and the shadowbox stagger are labeled typicals — measure your pattern.
Frequently asked questions
How many boards does board-on-board use?
Each board only covers its width minus the overlap, so a 5.5" board with a 1" overlap covers 4.5". At 100 ft that is about 267 boards exact, or 294 with a 10% waste margin — roughly 35% more than a butted run.
What overlap should I use?
About 1 inch is typical and hides the gaps that open as wood shrinks. Use more for a wetter climate or wider gaps risk, less to save lumber — but too little lets daylight through once the boards dry.
Is shadowbox the same as board-on-board?
Closely related. Board-on-board overlaps boards on one side; shadowbox alternates them front and back of the rails so the fence looks the same from both sides. Board counts are similar — this tool covers both.
Should I add waste?
Yes — keep the 10% default (or more). Fence boards are culled for warp, splits and knots, and you will trim boards at ends and corners. Confirm the board width against your actual product.