How this instrument works
A property's perimeter is the total distance around its boundary, and for fencing purposes it is the single most important starting number: it sets the total linear footage of material a job needs before anyone counts individual pickets, panels or posts. For a simple lot shape, that distance is nothing more than the sum of each straight side's length.
This instrument handles up to four sides directly, covering the two most common residential lot shapes: a four-sided lot (rectangular or an irregular quadrilateral) using all four fields, or a three-sided triangular lot by leaving the fourth side at zero, which contributes nothing to the total. For a rectangular lot specifically, this reduces to the familiar formula perimeter = 2 × (length + width), since opposite sides share the same length.
A lot with more than four straight sides needs a small manual step: group the extra sides into pairs, add each pair together by hand, and enter the combined lengths into two of the four fields, or simply run the calculation twice and add the two perimeter results together. The underlying arithmetic never changes — perimeter is always just every boundary length added together — only how many fields you need to fill in changes with the shape.
- Enter Side 1 length (ft) through Side 3 length (ft) for a triangular lot's three boundaries, or all four fields for a four-sided lot.
- For a triangular lot, set Side 4 length (ft, 0 if triangular) to 0 so it doesn't add to the total.
- Read Total fence perimeter (ft) directly — it updates the instant any side changes.
- For a lot with more than four sides, combine collinear or adjacent sides by hand first, or run the calculation more than once and add the results together.
Worked example — a 100 ft × 150 ft rectangular lot
Enter 100 into Side 1 length (ft), 150 into Side 2 length (ft), 100 into Side 3 length (ft) and 150 into Side 4 length (ft, 0 if triangular) — a rectangular lot with two 100 ft sides and two 150 ft sides. Total fence perimeter (ft) reads 500: 100 + 150 + 100 + 150 = 500 ft exactly.
That matches the familiar rectangle shortcut of 2 × (length + width) = 2 × (100 + 150) = 500 ft, since a rectangle's opposite sides are always equal — this instrument's plain sum-of-four-sides formula gives the identical answer without requiring that shortcut to be remembered.
Questions
How do I calculate perimeter for a triangular lot?
Enter the three actual side lengths into Side 1, Side 2 and Side 3, and set Side 4 length (ft, 0 if triangular) to 0 — since adding zero doesn't change the total, the instrument correctly returns the sum of just the three real sides. This avoids needing a separate formula for triangular versus rectangular lots.
What if my lot has more than four sides?
Combine sides in pairs by hand before entering them — for example, add two adjacent short sides on the same edge of the property into a single combined length — or simply calculate the perimeter of one section of the lot, note the result, calculate the remaining section separately, and add the two totals together. The formula itself is always just addition, so any shape can be broken down this way.
Does this account for gates, corner posts or overlap at corners?
No — this instrument returns the raw geometric perimeter only, the total distance around the boundary. It doesn't subtract for gate openings, add extra length for post overlap at corners, or account for a fence line that doesn't sit exactly on the property boundary; those adjustments happen in a separate materials estimate built on top of this perimeter figure.
Is this the same as the rectangle formula perimeter = 2(length + width)?
Yes, for a rectangular lot specifically — entering length twice (as Side 1 and Side 3) and width twice (as Side 2 and Side 4) and summing all four gives the identical result as 2 × (length + width), since a rectangle's opposite sides are equal by definition. This instrument's plain sum works for that case and for irregular quadrilaterals where the shortcut doesn't apply.
Should each side be the property line, or where the fence will actually sit?
Use whichever line the fence will actually follow, since that's the length of material you'll need — this is often the same as the property line, but not always, if the fence is deliberately set back from the boundary. Measure the real intended fence path for each side rather than assuming it matches a legal property line exactly.