Gutter Calculator
Gutter sections, downspouts, and hangers for your roofline.
Input sheet
DIY at your own risk. Calcora's calculators and guides are general estimates and information only — not professional, engineering, legal, or safety advice. Always verify local building codes and permit requirements, and hire a licensed pro for electrical, gas, plumbing, structural, or any work you're not fully comfortable doing yourself.
Gutter jobs are counted in three parts: the sections of gutter along the eaves, the downspouts that drain them, and the hangers that hold everything up. This calculator sizes all three from one number — the total run.
How it works
Sectional gutter comes in 10 ft lengths. One downspout serves every 30–40 ft of run, and hangers go every 24 in.
Sectional gutter sells in 10 ft lengths, so sections are the run divided by 10, rounded up. Seams get joined and sealed; every cut end takes an end cap, and every downspout location takes a drop outlet.
Downspout count uses the drainage rule of one downspout per 30–40 ft of gutter run. Fewer means water outruns the outlet in a hard rain and sheets over the front edge. Hangers go every 24 in — closer (16 in) in snow country where ice loads the run.
Sections = run ÷ 10 (rounded up); downspouts = run ÷ 35 (rounded up, minimum 1); hangers = run ÷ 2 ft.
Worked examples
A full perimeter of 120 ft of gutter. → 12 sections, 4 downspouts, 60 hangers.
120 ÷ 10 = 12 sections; 120 ÷ 35 = 3.4 → 4 downspouts; 120 × 12 ÷ 24 = 60 hangers.
One 60 ft rear eave. → 6 sections, 2 downspouts, 30 hangers.
60 ÷ 10 = 6; 60 ÷ 35 = 1.7 → 2 downspouts, one at each end with the slope split between them.
Tips & gotchas
- Slope gutter about ¼ in per 10 ft toward each downspout; long runs peak in the middle and drain both ways.
- Each downspout also needs elbows (usually three) and straps — count them separately from the 10 ft downspout stock.
- 5 in K-style handles most roofs; jump to 6 in when a large or steep roof concentrates a lot of water on one run.
FAQ
What size gutter do I need?
5 in K-style handles most homes; go 6 in for large or steep roofs that dump a lot of water fast.
Sectional or seamless?
Sectional is DIY-friendly and cheap; seamless is roll-formed on site to the exact run with no mid-run joints — fewer leak points, but it requires the truck and crew.
Where should downspouts discharge?
At least 4–6 ft away from the foundation, onto splash blocks or into extensions. A gutter that dumps at the wall is worse than no gutter for a basement.
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