Board-on-Board Fence Calculator

How to use the board-on-board fence calculator

What this calculator does

This tool estimates the core lumber quantities for a straight board-on-board privacy fence: sections, posts, rails, pickets, post stock length, actual section length, and the effective horizontal step between overlapping pickets. It is useful for early material takeoffs, comparing board widths, checking how overlap affects picket count, and creating a reproducible spreadsheet for a supplier quote. It does not design footings, verify wind loads, size structural members, account for gates or corners, or replace local code and site-specific engineering.

When to use it

Use it while budgeting a new privacy fence, comparing six-foot and eight-foot post spacing, deciding between common picket widths, or checking whether a larger overlap materially increases the lumber order. It also helps when you want a clean baseline before adding waste, gate framing, corner bracing, concrete, fasteners, or finish.

How to calculate

1. The calculator opens with a complete 100 ft demonstration fence, so the results and Download Excel button work immediately.
2. Replace Fence length, Maximum post spacing, and Fence height with your measured dimensions. Select feet or meters beside each field.
3. Enter Rails per section, then provide the actual Picket width and intended Picket overlap in inches or millimeters.
4. Read the live material estimate and the breakdown table. Counts always round upward because partial posts, rails, and pickets cannot complete the run.
5. Select Download Excel to export the current validated model. Reset clears the demonstration and all calculated state; Excel export then remains unavailable until every required field is complete and valid again.

Input guide

Fence length is required and accepts a positive decimal in feet or meters; 100 ft is the startup example. Increasing it raises every material count. Measure the actual fence centerline rather than lot area. Maximum post spacing is required and accepts a positive decimal in feet or meters; 8 ft is common in preliminary estimates. A smaller value creates more sections and posts. Do not treat this as an approved structural spacing without checking site conditions.

Fence height is required and accepts a positive decimal in feet or meters; the example uses 6 ft. It drives the estimated post stock length, calculated as 1.5 times visible fence height. Rails per section is a required whole number from 1 to 12; the example uses 3. More rails increase the rail total linearly. Picket width is the required actual face width, not a nominal lumber name; the example uses 5.5 in. Picket overlap is required, must be positive, and must stay below picket width; the example uses 1.25 in. A larger overlap reduces the effective step and increases picket count. Wood changes dimension with moisture, so consult the USDA Forest Products Laboratory discussion of drying, moisture content, and dimensional change before choosing a final overlap.

Output guide

Total pickets is the rounded-up board count for the full run. Number of sections is the rounded-up count of bays formed by the maximum spacing. Number of posts equals sections plus one for a straight open run. Number of rails equals sections multiplied by rails per section. Post length is an estimating rule of 1.5 times fence height, leaving one-third of the post below grade. Actual section length divides the full run evenly across the rounded section count, so it will never exceed the chosen maximum spacing. Effective picket step equals picket width minus overlap. These are planning estimates, not purchase recommendations; zero or missing values produce no model, while high counts usually indicate a long run, close posts, narrow boards, or heavy overlap.

Worked example

For the startup values, 100 ft divided by 8 ft equals 12.5, so the calculator rounds up to 13 sections and then adds one end post for 14 posts. Three rails per section produce 39 rails. The 5.5 in picket minus 1.25 in overlap gives a 4.25 in effective step. Converting 100 ft to 1,200 in and applying the board-on-board formula gives (1,200 – 5.5) ÷ 4.25 + 1 = 282.06, which rounds up to 283 pickets. The post stock estimate is 1.5 × 6 ft = 9 ft. The live page and workbook use these same formulas.