Fence on a Slope: Racked or Stepped, Rail Length and Cut Angle

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Opens on the book's own fence. Change any number to your own and press Calculate.

Start from fills the boxes below

Slope of the ground %

Bays down the slope

Post spacing mm, center to center

Post width mm

Rail width mm, for the square-cut check

Post above ground (flat) mm

Panel rack limit degrees, optional (from the maker)

Enter the slope and press Calculate.

The formula

Fall per bay = post spacing × slope
Racked rail = clear span × √(1 + slope²); cut each end at arctan(slope)
Stepped: step = spacing × slope; the triangle under each panel = ½ × span × (span × slope)
A stepped post stands one step taller on its downhill side

The book's worked example, Chapter 6. At 5 %, Route A falls 120 mm a bay and Route B 90 mm. Racked, Route A's 2,311 mm span needs a rail of 2,313.89 mm, 2.89 mm longer, with ends cut at 2.86°; Route B's is 1,713.14 mm. Stepped prefab 8 ft panels would step 126.4 mm a bay and leave a 0.149 m² triangle under each.

Prefab panels rack only so far: the maker states the limit in degrees. Past it, step the panels or build in place. Prices are illustrative US home-center prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.