Fence Set-Out: Post Centers from Zero, 3-4-5 and the Slope

Home › Calculators › Fence Set-Out

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

Start from fills the boxes below

Gate posts, center to center mm; 0 if no gate

Post spacing mm

Fence bays

The fall

Fall along the fence mm, read at the stakes

Over a length of mm

String height at the gate mm above the ground

A corner (3-4-5) and a rectangle

Scale the 3-4-5 by m: 0.3 gives 0.9-1.2-1.5

Diagonal you measured m, optional

Rectangle length m, e.g. an enclosure

Rectangle width m

Enter the spacing and press Calculate.

The formula

Post centers from zero: G1 = 0, G2 = the gate's center-to-center, then G2 + spacing × 1, 2, 3 …
Slope = fall ÷ length; angle = arctan(slope); inches per foot = slope × 12
Drop at each post = slope × its distance from G2 (the gate bay is kept level)
3-4-5 scaled: 3s, 4s, 5s. Diagonal of a rectangle = √(length² + width²)

The book's worked example, Chapter 2. Route A's posts sit at 0, 1,089, 3,489, 5,889, 8,289 mm from the hinge post (G1 to P3); Route B's at 0, 1,114.5, 2,914.5, 4,714.5, 6,514.5, 8,314.5 mm. The ground falls 360 mm over 7,200 mm: 5 %, 2.86°, or 0.6 in per foot, so the string reads 150, 150, 270, 390, 510 mm above the ground at Route A's posts.

Find the boundary first: the whole fence, footings included, should stand on your side of it. 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.