Downspout Calculator
Downspout Count & Sizing
Calculate how many downspouts your gutter system needs
Downspout Materials List
Calculate downspout materials and extensions needed
Formula
Downspouts = Max(Roof Area / Capacity, Gutter Length / 35) | Length Per Unit = Building Height + 2 ft | Elbows = 3 per downspout
Frequently Asked Questions
How many downspouts do I need?
As a general rule, install one downspout for every 20-35 feet of gutter. A typical home with 120 feet of gutter needs 4-6 downspouts. Increase downspouts in heavy rainfall areas or for steep roofs.
Where should downspouts be placed?
Place downspouts at the lowest points of gutter runs, near corners, and at the ends of gutter sections. Never run more than 40 feet of gutter to a single downspout. Aim to direct water away from foundations, driveways, and walkways.
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