Fence slope calculator
Adjust your fence run for a graded yard: slope-adjusted length from the horizontal run, plus a rack-versus-step sanity check.
Fence calculator
Enter your specs. Every result updates live and shows its formula.
Overview
A fence that follows the grade is slightly longer than the horizontal distance between its endpoints, exactly like a ramp is longer than the flat footprint it crosses. This calculator converts your horizontal run and slope percentage into the slope-adjusted length the material actually has to span.
It then leaves the design choice to you: raking panels to follow a gentle, even grade continuously, or stepping each panel level at the posts for a steeper, uneven grade or for vinyl, which cannot be racked at an angle.
Common mistakes
- Ordering material for the horizontal distance on a graded run, which comes up short by the slope-adjusted amount.
- Raking vinyl or other rigid panel systems that are built to be stepped, not angled across a grade.
- Updating the length but not the post count, when posts still sit at their horizontal spacing along the run regardless of grade.
Related calculators
- Fence perimeter calculator Get the total perimeter feet and the post sections that length implies for a rectangular yard, with the spacing math shown.
- Wood fence calculator Calculate posts, rails, pickets and concrete for a pressure-treated pine, cedar or redwood fence. Every formula shown, cost optional.
- Chain link fence calculator Calculate line posts, terminal posts, top rail and concrete for a chain link fence run, with 10 foot post spacing as the default.
Related reading
In-depth guides
Frequently asked questions
What is the formula for slope-adjusted fence length?
Convert the slope percent to an angle with arctan(slope percent divided by 100), then divide the horizontal run by the cosine of that angle. A 100 foot run on a 25 percent grade comes out to about 103 feet of built fence.
How much longer is a fence on a slope?
Gently, more than you might expect less than you fear: at a 5 percent grade the built length is only about 0.1 percent over the horizontal, and at 25 percent it grows to roughly 3 percent, about 3 extra feet per 100. Steep and long is when it starts to matter.
Should I rack or step a fence on a slope?
Rake it when the grade is gentle and even and the material allows an angle, which most wood privacy does. Step it when the grade is steep or uneven, or when the product is a fixed panel like vinyl that can only sit level, dropping each panel at its post.
What slope percentage needs stepping?
There is no universal cutoff, but the practical band used in the field is that most panel systems start to look forced once a run exceeds roughly 10 to 15 percent grade, and racking matters less than the material: check vinyl and panel specs specifically, since they step by design.
Does slope change the post count?
No on its own. Posts are still set at your horizontal spacing measured along the run, so the slope riddle is the panels and boards spanning the grade, not the post spacing itself.
Does the slope-adjusted length change pickets or boards?
Yes: boards and pickets cover the built length along the grade, so the adjusted run feeds the board math. That is why the wood, picket and rail calculators all take a run length you can insert from this result.
What is the fastest way to measure slope percent?
Measure the rise (vertical change) and the horizontal run between the two endpoints, then compute rise over run times 100. A 2 foot rise over a 40 foot run is a 5 percent grade, the same number this calculator takes as its input.
Do corner and gate posts change on a slope?
Same posts, same rules. Gates still want their two posts and a level sill, corners still take tension in both directions, and stepping compounds the corner post load at the low end of each step where the panel weight lands on it.