Gutter Calculator
Linear feet of gutter, number of sections and downspouts needed for a roof edge.
Gutter jobs are quoted by the linear foot but assembled in sections, and the two numbers diverge at every corner. A 120 ft run around three sides of a house is not twelve sections — corners consume material, and each downspout outlet interrupts the run.
The number that matters most is not length but outlet count. One downspout per 35 ft of gutter is the working rule; 40 ft is the absolute maximum. A roof that dumps 800 sq ft of water into a single outlet will overflow in any serious rain, regardless of how well the gutter itself is installed.
How this calculator works
Every field is editable and the result updates as you type — nothing is submitted anywhere, all the maths runs in your browser. That matters for a number you are about to spend money on: you can see exactly which input moved the answer, and by how much.
What this calculation assumes
Assumes a single-storey run with normal access and no fascia repair. Two-storey installation, rotted fascia, gutter guards and underground drainage are excluded, and any of them can double the installed price.
Treat the result as an order-of-magnitude check rather than a final quantity. Product packaging changes, regional labour rates vary by a factor of two, and no calculator has seen your actual site.
Frequently asked questions
How many downspouts do I need?
One per 35 ft of gutter run, with no more than 40 ft between them, and one at the low end of every run. A 120 ft perimeter on a typical hip roof usually needs four. Too few downspouts is the single most common reason gutters overflow at the fascia.
5 inch or 6 inch gutters?
Five inch K-style handles most residential roofs up to about 2,000 sq ft of roof area. Go to six inch for larger roofs, steep pitches, long runs without outlets, or heavy rainfall regions. The cost difference is modest next to the cost of fixing water damage.
Seamless or sectional gutters?
Seamless, if there is a fabricator in your area. They are formed on site in one continuous run, so the only joints are at corners and outlets — which is where leaks happen anyway. Sectional gutters have a joint every 10 ft, and each one is a future leak.
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