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Perimeter calculator
The linear-foot run around a rectangular plan — what baseboard, top plate, continuous footings, and fence lines are measured by.
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How it’s computed
Perimeter = 2 × (length + width), in linear feet (lf), exact decimal arithmetic.
Decimal-exact and deterministic: identical inputs always return identical results. This is the same math Ask Donnie’s estimating engine runs — not an approximation, and never a language model doing arithmetic.
Common questions
What do contractors use perimeter for?
Anything sold or installed by the running foot: baseboard and trim, wall plates, continuous footings, drip edge, siding starter, fencing.
My building isn't a rectangle.
Sum the individual side lengths — perimeter is just the total run. This calculator handles the rectangular case; add wings separately.
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