What this calculator does
Board-on-board fence works out boards, posts and rails for a board-on-board fence, from the board overlap. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaBoards = ⌊fence length / (board width − overlap)⌋ + 1, since each board overlaps the gap of the one before it
The inputs explained
| Field | What to enter |
|---|---|
| Fence length (m) | A number, measured in m. Starts at 20. |
| Fence height (m) | A number, measured in m. Starts at 1.8. |
| Board width (mm) | A number, measured in mm. Starts at 140. |
| Overlap (mm) | A number, measured in mm. Starts at 25. |
| Post spacing (m) | A number, measured in m. Starts at 2.4. |
| Rails per bay | A number. Starts at 3. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with fence length
Every other input is held at the calculator’s starting values while fence length varies. Select any row to load that scenario into the calculator.